{"id":389,"date":"2026-07-06T18:16:17","date_gmt":"2026-07-06T18:16:17","guid":{"rendered":"https:\/\/sigmadesk.app\/blog\/?p=389"},"modified":"2026-07-06T21:34:47","modified_gmt":"2026-07-06T21:34:47","slug":"cpk-values-sigma-levels","status":"publish","type":"post","link":"https:\/\/sigmadesk.app\/blog\/cpk-values-sigma-levels\/","title":{"rendered":"Cpk 1.33, 1.67, 2.00 | PPM Rates &amp; Sigma Levels"},"content":{"rendered":"\n<p class=\"wp-block-paragraph\">This article breaks down what each <strong>Cpk<\/strong> level really means in terms of sigma levels, defect rates, and practical risk, so you can set capability targets with confidence instead of habit.<\/p>\n\n\n\n<figure class=\"wp-block-embed is-type-video is-provider-youtube wp-block-embed-youtube wp-embed-aspect-16-9 wp-has-aspect-ratio\"><div class=\"wp-block-embed__wrapper\">\n<iframe loading=\"lazy\" title=\"Cpk 1.33 vs 1.67 vs 2.00 Explained | PPM Defect Rates &amp; Sigma Levels\" width=\"660\" height=\"371\" src=\"https:\/\/www.youtube.com\/embed\/lGt2tH1KVMQ?feature=oembed\" frameborder=\"0\" allow=\"accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share\" referrerpolicy=\"strict-origin-when-cross-origin\" allowfullscreen><\/iframe>\n<\/div><\/figure>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<p class=\"wp-block-paragraph\">A Cpk of <strong>1.33<\/strong> is a four sigma process (\u2248 63 defective parts per million), a Cpk of <strong>1.67<\/strong> is a five sigma process (&lt; 1 PPM), and a Cpk of <strong>2.00<\/strong> is a six sigma process (\u2248 2 parts per billion short-term, or 3.4 PPM after the assumed 1.5\u03c3 long-term shift). Cpk 1.33 is the common minimum for ongoing production; 1.67 is required for critical characteristics and new launches; 2.00 defines a six sigma process.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Three numbers appear over and over in <a href=\"https:\/\/sigmadesk.app\/blog\/process-capability-analysis\/\">process capability analysis<\/a>: <strong>1.33, 1.67, and 2.00<\/strong>. You will find them in customer specifications, supplier quality agreements, PPAP submissions, and audit checklists across virtually every industry. <\/p>\n\n\n\n<h2 class=\"wp-block-heading has-text-align-center\" style=\"font-size:32px\">What Cpk Actually Measures<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Cpk measures how well your process fits inside the specification limits <strong>while accounting for centering<\/strong>. It takes the distance from the process mean to the <em>nearest<\/em> specification limit and divides it by three <a href=\"https:\/\/sigmadesk.app\/blog\/standard-deviation\/\">standard deviations<\/a>:<\/p>\n\n\n\n<p class=\"has-text-align-center wp-block-paragraph\" style=\"font-size:22px\">Cpk = min ( (USL \u2212 \u03bc) \/ 3\u03c3 , (\u03bc \u2212 LSL) \/ 3\u03c3 )<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A higher Cpk means more breathing room between your process variation and the point where parts become defective. Unlike Cp, Cpk penalizes an off-center process \u2014 that distinction is covered in detail in <a href=\"https:\/\/sigmadesk.app\/blog\/cp-and-cpk-difference\/\">the difference between Cp and Cpk<\/a>. Every threshold discussed in this article is simply a statement about <strong>how much of that breathing room your customer expects<\/strong>.<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"576\" src=\"https:\/\/sigmadesk.app\/blog\/wp-content\/uploads\/2026\/07\/image-11-1024x576.png\" alt=\"Cpk formula Cpk = min((USL \u2212 \u03bc)\/3\u03c3, (\u03bc \u2212 LSL)\/3\u03c3) illustrated with a normal distribution curve between the lower and upper specification limits\" class=\"wp-image-390\" srcset=\"https:\/\/sigmadesk.app\/blog\/wp-content\/uploads\/2026\/07\/image-11-1024x576.png 1024w, https:\/\/sigmadesk.app\/blog\/wp-content\/uploads\/2026\/07\/image-11-300x169.png 300w, https:\/\/sigmadesk.app\/blog\/wp-content\/uploads\/2026\/07\/image-11-768x432.png 768w, https:\/\/sigmadesk.app\/blog\/wp-content\/uploads\/2026\/07\/image-11-1536x864.png 1536w, https:\/\/sigmadesk.app\/blog\/wp-content\/uploads\/2026\/07\/image-11-2048x1152.png 2048w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><figcaption class=\"wp-element-caption\">The Cpk formula: the distance from the process mean to the nearest specification limit, divided by three standard deviations<\/figcaption><\/figure>\n\n\n\n<h3 class=\"wp-block-heading has-text-align-left\" style=\"font-size:22px\">What is PPM?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">PPM stands for <strong>parts per million<\/strong> \u2014 a way of expressing defect rates on a common scale. A PPM of 63 means that out of every one million parts produced, roughly 63 are expected to fall outside the specification limits. The lower the PPM, the fewer defects escape your process.<\/p>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\" style=\"font-size:22px\">PPM = (Defective Parts \/ Total Parts) \u00d7 1,000,000<\/p>\n<\/blockquote>\n\n\n\n<p class=\"wp-block-paragraph\">As Cpk increases, the tail of the <a href=\"https:\/\/sigmadesk.app\/blog\/normal-distribution-the-bell-curve\/\">normal distribution<\/a> beyond the specification limit shrinks, and the PPM value drops with it.<\/p>\n\n\n\n<h2 class=\"wp-block-heading has-text-align-center\" style=\"font-size:32px\">Cpk = 1.33: The Four Sigma Floor<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">A Cpk of 1.33 corresponds to a <strong>four sigma process<\/strong>: the nearest specification limit sits four standard deviations away from the process mean. In the short term, that translates to a defect rate of roughly <strong>63 parts per million<\/strong>.<\/p>\n\n\n\n<!-- ============================================================\n  WIDGET 1 \u2014 Cpk = 1.33 (place after the \"Cpk = 1.33: The Four Sigma Floor\" intro paragraph)\n  mu = 50.0 (centered), sigma = 0.10  \u2192  USL is 4\u03c3 away  \u2192  Cpk = 1.33\n============================================================ -->\n<div style=\"max-width:640px;margin:0 auto;\">\n<div style=\"width:100%;height:280px;\"><canvas id=\"sd-cpk133\"><\/canvas><\/div>\n<div style=\"display:flex;gap:20px;margin-top:12px;font-size:13px;font-family:system-ui,sans-serif;color:#666;flex-wrap:wrap;justify-content:center;\">\n  <span style=\"display:flex;align-items:center;gap:6px;\"><span style=\"width:28px;border-top:2px dashed #e34948;display:inline-block;\"><\/span>USL \/ LSL<\/span>\n  <span style=\"display:flex;align-items:center;gap:6px;\"><span style=\"width:28px;border-top:2px dashed #1baf7a;display:inline-block;\"><\/span>Mean (X\u0304)<\/span>\n  <span style=\"display:flex;align-items:center;gap:6px;\"><span style=\"width:16px;height:12px;background:rgba(42,120,214,0.20);border:2px solid #2a78d6;display:inline-block;border-radius:2px;\"><\/span>Process distribution<\/span>\n  <span style=\"display:flex;align-items:center;gap:6px;\"><span style=\"width:28px;border-top:2px solid #555;display:inline-block;\"><\/span>Sigma span (X\u0304 \u2192 USL)<\/span>\n<\/div>\n<p style=\"margin-top:10px;font-size:13px;font-family:system-ui,sans-serif;color:#888;font-style:italic;text-align:center;\">Cpk = 1.33 process capability chart \u2014 the nearest specification limit (USL) sits 4\u03c3 from the mean; expected defect rate \u2248 63 PPM<\/p>\n<\/div>\n<script>\n(function(){\n  function init(){\n    var LSL=49.5,USL=50.5,mu=50.0,sig=0.125,yMax=3.6,nSig=4;\n    function pdf(x){return Math.exp(-0.5*Math.pow((x-mu)\/sig,2))\/(sig*Math.sqrt(2*Math.PI));}\n    var pts=[];for(var i=0;i<=100;i++){var x=49.4+1.2*i\/100;pts.push({x:+(x.toFixed(3)),y:+(pdf(x).toFixed(5))});}\n    function vLine(xv,col){return{showLine:true,data:[{x:xv,y:0},{x:xv,y:yMax*0.90}],borderColor:col,borderWidth:1.5,borderDash:[5,5],pointRadius:0,fill:false,tension:0};}\n    var lp={id:'lbl_cpk133',afterDraw:function(c){\n      var ctx=c.ctx,xs=c.scales.x,ca=c.chartArea,t=ca.top+13;\n      ctx.save();ctx.font='bold 11px system-ui,sans-serif';ctx.textAlign='center';\n      ctx.fillStyle='#e34948';ctx.fillText('LSL',xs.getPixelForValue(LSL),t);ctx.fillText('USL',xs.getPixelForValue(USL),t);\n      ctx.fillStyle='#1baf7a';ctx.fillText('X\\u0304',xs.getPixelForValue(mu),t);\n      var y=ca.top+(ca.bottom-ca.top)*0.40;\n      var x1=xs.getPixelForValue(mu),x2=xs.getPixelForValue(USL);\n      ctx.strokeStyle='#555';ctx.fillStyle='#555';ctx.lineWidth=1.5;\n      ctx.beginPath();ctx.moveTo(x1+7,y);ctx.lineTo(x2-7,y);ctx.stroke();\n      ctx.beginPath();ctx.moveTo(x1,y);ctx.lineTo(x1+7,y-4);ctx.lineTo(x1+7,y+4);ctx.closePath();ctx.fill();\n      ctx.beginPath();ctx.moveTo(x2,y);ctx.lineTo(x2-7,y-4);ctx.lineTo(x2-7,y+4);ctx.closePath();ctx.fill();\n      for(var k=1;k<nSig;k++){\n        var xt=xs.getPixelForValue(mu+k*sig);\n        ctx.beginPath();ctx.moveTo(xt,y-4);ctx.lineTo(xt,y+4);ctx.stroke();\n      }\n      ctx.font='bold 13px system-ui,sans-serif';\n      ctx.fillText(nSig+'\\u03C3',(x1+x2)\/2,y-9);\n      ctx.restore();\n    }};\n    new Chart(document.getElementById('sd-cpk133'),{\n      type:'scatter',plugins:[lp],\n      data:{datasets:[\n        {showLine:true,data:pts,borderColor:'#2a78d6',borderWidth:2.5,backgroundColor:'rgba(42,120,214,0.18)',fill:'origin',pointRadius:0,tension:0.35},\n        vLine(LSL,'#e34948'),vLine(USL,'#e34948'),vLine(mu,'#1baf7a')\n      ]},\n      options:{responsive:true,maintainAspectRatio:false,\n        plugins:{legend:{display:false},tooltip:{enabled:false}},\n        scales:{\n          x:{type:'linear',min:49.4,max:50.6,ticks:{color:'#888',font:{size:11},stepSize:0.2,callback:function(v){return v.toFixed(1);}},grid:{color:'#eee'}},\n          y:{display:false,min:0,max:yMax}\n        }\n      }\n    });\n  }\n  if(!window._cjsQ)window._cjsQ=[];\n  if(window.Chart){init();return;}\n  window._cjsQ.push(init);\n  if(!window._cjsLoading){\n    window._cjsLoading=true;\n    var s=document.createElement('script');\n    s.src='https:\/\/cdnjs.cloudflare.com\/ajax\/libs\/Chart.js\/4.4.1\/chart.umd.js';\n    s.onload=function(){(window._cjsQ||[]).forEach(function(f){f();});window._cjsQ=[];};\n    document.head.appendChild(s);\n  }\n})();\n<\/script>\n\n\n\n<p class=\"wp-block-paragraph\">This is the most common minimum requirement in manufacturing, and for good reason. Compared with a barely capable process (Cpk = 1.00, or three sigma), it provides a full extra sigma of buffer. That buffer absorbs small shifts in the mean \u2014 from tool wear, material variation, or setup differences \u2014 before defects begin to appear.<\/p>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\" style=\"font-size:22px\">For most general-purpose characteristics, Cpk 1.33 is the accepted floor for ongoing production.<\/p>\n<\/blockquote>\n\n\n\n<h2 class=\"wp-block-heading has-text-align-center\" style=\"font-size:32px\">Cpk = 1.67: The Five Sigma Requirement<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">A Cpk of 1.67 raises the bar to <strong>five sigma<\/strong>, cutting the expected defect rate to <strong>under one part per million<\/strong>.<\/p>\n\n\n\n<!-- ============================================================\n  WIDGET 2 \u2014 Cpk = 1.67 (place after the \"Cpk = 1.67: The Five Sigma Requirement\" intro paragraph)\n  mu = 50.0 (centered), sigma = 0.08  \u2192  USL is 5\u03c3 away  \u2192  Cpk = 1.67\n============================================================ -->\n<div style=\"max-width:640px;margin:0 auto;\">\n<div style=\"width:100%;height:280px;\"><canvas id=\"sd-cpk167\"><\/canvas><\/div>\n<div style=\"display:flex;gap:20px;margin-top:12px;font-size:13px;font-family:system-ui,sans-serif;color:#666;flex-wrap:wrap;justify-content:center;\">\n  <span style=\"display:flex;align-items:center;gap:6px;\"><span style=\"width:28px;border-top:2px dashed #e34948;display:inline-block;\"><\/span>USL \/ LSL<\/span>\n  <span style=\"display:flex;align-items:center;gap:6px;\"><span style=\"width:28px;border-top:2px dashed #1baf7a;display:inline-block;\"><\/span>Mean (X\u0304)<\/span>\n  <span style=\"display:flex;align-items:center;gap:6px;\"><span style=\"width:16px;height:12px;background:rgba(42,120,214,0.20);border:2px solid #2a78d6;display:inline-block;border-radius:2px;\"><\/span>Process distribution<\/span>\n  <span style=\"display:flex;align-items:center;gap:6px;\"><span style=\"width:28px;border-top:2px solid #555;display:inline-block;\"><\/span>Sigma span (X\u0304 \u2192 USL)<\/span>\n<\/div>\n<p style=\"margin-top:10px;font-size:13px;font-family:system-ui,sans-serif;color:#888;font-style:italic;text-align:center;\">Cpk = 1.67 process capability chart \u2014 reduced variation puts the USL 5\u03c3 from the mean; expected defect rate &lt; 1 PPM<\/p>\n<\/div>\n<script>\n(function(){\n  function init(){\n    var LSL=49.5,USL=50.5,mu=50.0,sig=0.10,yMax=4.5,nSig=5;\n    function pdf(x){return Math.exp(-0.5*Math.pow((x-mu)\/sig,2))\/(sig*Math.sqrt(2*Math.PI));}\n    var pts=[];for(var i=0;i<=100;i++){var x=49.4+1.2*i\/100;pts.push({x:+(x.toFixed(3)),y:+(pdf(x).toFixed(5))});}\n    function vLine(xv,col){return{showLine:true,data:[{x:xv,y:0},{x:xv,y:yMax*0.90}],borderColor:col,borderWidth:1.5,borderDash:[5,5],pointRadius:0,fill:false,tension:0};}\n    var lp={id:'lbl_cpk167',afterDraw:function(c){\n      var ctx=c.ctx,xs=c.scales.x,ca=c.chartArea,t=ca.top+13;\n      ctx.save();ctx.font='bold 11px system-ui,sans-serif';ctx.textAlign='center';\n      ctx.fillStyle='#e34948';ctx.fillText('LSL',xs.getPixelForValue(LSL),t);ctx.fillText('USL',xs.getPixelForValue(USL),t);\n      ctx.fillStyle='#1baf7a';ctx.fillText('X\\u0304',xs.getPixelForValue(mu),t);\n      var y=ca.top+(ca.bottom-ca.top)*0.40;\n      var x1=xs.getPixelForValue(mu),x2=xs.getPixelForValue(USL);\n      ctx.strokeStyle='#555';ctx.fillStyle='#555';ctx.lineWidth=1.5;\n      ctx.beginPath();ctx.moveTo(x1+7,y);ctx.lineTo(x2-7,y);ctx.stroke();\n      ctx.beginPath();ctx.moveTo(x1,y);ctx.lineTo(x1+7,y-4);ctx.lineTo(x1+7,y+4);ctx.closePath();ctx.fill();\n      ctx.beginPath();ctx.moveTo(x2,y);ctx.lineTo(x2-7,y-4);ctx.lineTo(x2-7,y+4);ctx.closePath();ctx.fill();\n      for(var k=1;k<nSig;k++){\n        var xt=xs.getPixelForValue(mu+k*sig);\n        ctx.beginPath();ctx.moveTo(xt,y-4);ctx.lineTo(xt,y+4);ctx.stroke();\n      }\n      ctx.font='bold 13px system-ui,sans-serif';\n      ctx.fillText(nSig+'\\u03C3',(x1+x2)\/2,y-9);\n      ctx.restore();\n    }};\n    new Chart(document.getElementById('sd-cpk167'),{\n      type:'scatter',plugins:[lp],\n      data:{datasets:[\n        {showLine:true,data:pts,borderColor:'#2a78d6',borderWidth:2.5,backgroundColor:'rgba(42,120,214,0.18)',fill:'origin',pointRadius:0,tension:0.35},\n        vLine(LSL,'#e34948'),vLine(USL,'#e34948'),vLine(mu,'#1baf7a')\n      ]},\n      options:{responsive:true,maintainAspectRatio:false,\n        plugins:{legend:{display:false},tooltip:{enabled:false}},\n        scales:{\n          x:{type:'linear',min:49.4,max:50.6,ticks:{color:'#888',font:{size:11},stepSize:0.2,callback:function(v){return v.toFixed(1);}},grid:{color:'#eee'}},\n          y:{display:false,min:0,max:yMax}\n        }\n      }\n    });\n  }\n  if(!window._cjsQ)window._cjsQ=[];\n  if(window.Chart){init();return;}\n  window._cjsQ.push(init);\n  if(!window._cjsLoading){\n    window._cjsLoading=true;\n    var s=document.createElement('script');\n    s.src='https:\/\/cdnjs.cloudflare.com\/ajax\/libs\/Chart.js\/4.4.1\/chart.umd.js';\n    s.onload=function(){(window._cjsQ||[]).forEach(function(f){f();});window._cjsQ=[];};\n    document.head.appendChild(s);\n  }\n})();\n<\/script>\n\n\n\n<p class=\"wp-block-paragraph\">You will see this requirement on safety-critical or high-consequence characteristics, and it is the common expectation for <strong>new process launches in automotive under PPAP<\/strong>, where a Ppk of 1.67 is typically demanded before production approval.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The logic is simple: new processes have not yet demonstrated long-term stability, and critical features cannot tolerate the risk that a modest mean shift would create at lower capability levels. The extra sigma of margin is insurance against the unknown.<\/p>\n\n\n\n<h2 class=\"wp-block-heading has-text-align-center\" style=\"font-size:32px\">Cpk = 2.00: The Six Sigma Definition<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">A Cpk of 2.00 is the literal definition of a <strong>six sigma process<\/strong>: the nearest specification limit is six standard deviations from the mean, and the short-term defect rate drops to about <strong>two parts per billion<\/strong>.<\/p>\n\n\n\n<!-- ============================================================\n  WIDGET 3 \u2014 Cpk = 2.00 (place after the \"Cpk = 2.00: The Six Sigma Definition\" intro paragraph)\n  mu = 50.0 (centered), sigma = 0.0667  \u2192  USL is 6\u03c3 away  \u2192  Cpk = 2.00\n============================================================ -->\n<div style=\"max-width:640px;margin:0 auto;\">\n<div style=\"width:100%;height:280px;\"><canvas id=\"sd-cpk200\"><\/canvas><\/div>\n<div style=\"display:flex;gap:20px;margin-top:12px;font-size:13px;font-family:system-ui,sans-serif;color:#666;flex-wrap:wrap;justify-content:center;\">\n  <span style=\"display:flex;align-items:center;gap:6px;\"><span style=\"width:28px;border-top:2px dashed #e34948;display:inline-block;\"><\/span>USL \/ LSL<\/span>\n  <span style=\"display:flex;align-items:center;gap:6px;\"><span style=\"width:28px;border-top:2px dashed #1baf7a;display:inline-block;\"><\/span>Mean (X\u0304)<\/span>\n  <span style=\"display:flex;align-items:center;gap:6px;\"><span style=\"width:16px;height:12px;background:rgba(42,120,214,0.20);border:2px solid #2a78d6;display:inline-block;border-radius:2px;\"><\/span>Process distribution<\/span>\n  <span style=\"display:flex;align-items:center;gap:6px;\"><span style=\"width:28px;border-top:2px solid #555;display:inline-block;\"><\/span>Sigma span (X\u0304 \u2192 USL)<\/span>\n<\/div>\n<p style=\"margin-top:10px;font-size:13px;font-family:system-ui,sans-serif;color:#888;font-style:italic;text-align:center;\">Cpk = 2.00 process capability chart \u2014 the six sigma process: the USL sits 6\u03c3 from the mean; short-term defect rate \u2248 2 PPB<\/p>\n<\/div>\n<script>\n(function(){\n  function init(){\n    var LSL=49.5,USL=50.5,mu=50.0,sig=0.0833,yMax=5.4,nSig=6;\n    function pdf(x){return Math.exp(-0.5*Math.pow((x-mu)\/sig,2))\/(sig*Math.sqrt(2*Math.PI));}\n    var pts=[];for(var i=0;i<=100;i++){var x=49.4+1.2*i\/100;pts.push({x:+(x.toFixed(3)),y:+(pdf(x).toFixed(5))});}\n    function vLine(xv,col){return{showLine:true,data:[{x:xv,y:0},{x:xv,y:yMax*0.90}],borderColor:col,borderWidth:1.5,borderDash:[5,5],pointRadius:0,fill:false,tension:0};}\n    var lp={id:'lbl_cpk200',afterDraw:function(c){\n      var ctx=c.ctx,xs=c.scales.x,ca=c.chartArea,t=ca.top+13;\n      ctx.save();ctx.font='bold 11px system-ui,sans-serif';ctx.textAlign='center';\n      ctx.fillStyle='#e34948';ctx.fillText('LSL',xs.getPixelForValue(LSL),t);ctx.fillText('USL',xs.getPixelForValue(USL),t);\n      ctx.fillStyle='#1baf7a';ctx.fillText('X\\u0304',xs.getPixelForValue(mu),t);\n      var y=ca.top+(ca.bottom-ca.top)*0.40;\n      var x1=xs.getPixelForValue(mu),x2=xs.getPixelForValue(USL);\n      ctx.strokeStyle='#555';ctx.fillStyle='#555';ctx.lineWidth=1.5;\n      ctx.beginPath();ctx.moveTo(x1+7,y);ctx.lineTo(x2-7,y);ctx.stroke();\n      ctx.beginPath();ctx.moveTo(x1,y);ctx.lineTo(x1+7,y-4);ctx.lineTo(x1+7,y+4);ctx.closePath();ctx.fill();\n      ctx.beginPath();ctx.moveTo(x2,y);ctx.lineTo(x2-7,y-4);ctx.lineTo(x2-7,y+4);ctx.closePath();ctx.fill();\n      for(var k=1;k<nSig;k++){\n        var xt=xs.getPixelForValue(mu+k*sig);\n        ctx.beginPath();ctx.moveTo(xt,y-4);ctx.lineTo(xt,y+4);ctx.stroke();\n      }\n      ctx.font='bold 13px system-ui,sans-serif';\n      ctx.fillText(nSig+'\\u03C3',(x1+x2)\/2,y-9);\n      ctx.restore();\n    }};\n    new Chart(document.getElementById('sd-cpk200'),{\n      type:'scatter',plugins:[lp],\n      data:{datasets:[\n        {showLine:true,data:pts,borderColor:'#2a78d6',borderWidth:2.5,backgroundColor:'rgba(42,120,214,0.18)',fill:'origin',pointRadius:0,tension:0.35},\n        vLine(LSL,'#e34948'),vLine(USL,'#e34948'),vLine(mu,'#1baf7a')\n      ]},\n      options:{responsive:true,maintainAspectRatio:false,\n        plugins:{legend:{display:false},tooltip:{enabled:false}},\n        scales:{\n          x:{type:'linear',min:49.4,max:50.6,ticks:{color:'#888',font:{size:11},stepSize:0.2,callback:function(v){return v.toFixed(1);}},grid:{color:'#eee'}},\n          y:{display:false,min:0,max:yMax}\n        }\n      }\n    });\n  }\n  if(!window._cjsQ)window._cjsQ=[];\n  if(window.Chart){init();return;}\n  window._cjsQ.push(init);\n  if(!window._cjsLoading){\n    window._cjsLoading=true;\n    var s=document.createElement('script');\n    s.src='https:\/\/cdnjs.cloudflare.com\/ajax\/libs\/Chart.js\/4.4.1\/chart.umd.js';\n    s.onload=function(){(window._cjsQ||[]).forEach(function(f){f();});window._cjsQ=[];};\n    document.head.appendChild(s);\n  }\n})();\n<\/script>\n\n\n\n<h3 class=\"wp-block-heading\" style=\"font-size:22px\">Isn't Six Sigma 3.4 Defects per Million?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">You have probably heard six sigma linked to a different number: 3.4 defects per million. So why the gap between two parts per <em>billion<\/em> and 3.4 parts per <em>million<\/em>?<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Because the six sigma concept assumes a <strong>long-term 1.5 sigma shift<\/strong> in the process mean. Over months of production, tooling, materials, and operators drift the process center. That shift turns a short-term Cpk of 2.00 into a long-term Ppk of 1.50 \u2014 the distinction between short-term and long-term indices is explained in <a href=\"https:\/\/sigmadesk.app\/blog\/process-capability-vs-performance-cp-cpk-vs-pp-ppk\/\">Cpk vs Ppk<\/a> \u2014 and it is this long-term Ppk of 1.50 that produces the famous 3.4 defects-per-million figure.<\/p>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\" style=\"font-size:22px\">Short-term Cpk = 2.00 \u2192 apply the 1.5\u03c3 shift \u2192 long-term Ppk = 1.50 \u2192 3.4 PPM.<\/p>\n<\/blockquote>\n\n\n\n<h2 class=\"wp-block-heading has-text-align-center\" style=\"font-size:32px\">The Cpk Thresholds<\/h2>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th>Cpk<\/th><th>Sigma Level (short-term)<\/th><th>Expected Defect Rate<\/th><th>Typical Use<\/th><\/tr><\/thead><tbody><tr><td>1.33<\/td><td>4\u03c3<\/td><td>\u2248 63 PPM<\/td><td>General characteristics, ongoing production<\/td><\/tr><tr><td>1.67<\/td><td>5\u03c3<\/td><td>&lt; 1 PPM<\/td><td>Safety-critical features, new launches (PPAP)<\/td><\/tr><tr><td>2.00<\/td><td>6\u03c3<\/td><td>\u2248 2 PPB short-term (3.4 PPM with 1.5\u03c3 shift)<\/td><td>Six sigma programs, extreme failure cost<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">Notice the pattern: each step of one third in Cpk adds a <strong>full standard deviation of margin<\/strong>. That extra sigma is not about the defects you see today. It is insurance against tool wear, material lot changes, and operator variation that will shift your mean over time.<\/p>\n\n\n\n<h2 class=\"wp-block-heading has-text-align-center\" style=\"font-size:32px\">Which Cpk Target Should You Use?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Match the requirement to the <strong>consequence of failure<\/strong>:<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th>Situation<\/th><th>Recommended Target<\/th><\/tr><\/thead><tbody><tr><td>General characteristics in stable production<\/td><td>Cpk \u2265 1.33<\/td><\/tr><tr><td>Critical characteristics, new launches, safety or regulatory features<\/td><td>Cpk \u2265 1.67<\/td><\/tr><tr><td>Six sigma programs; extreme downstream failure cost<\/td><td>Cpk \u2265 2.00<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">And a word of caution in the other direction: chasing a higher Cpk than the risk justifies ties up capital in tighter tolerances, more expensive equipment, and slower cycle times.<\/p>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\" style=\"font-size:22px\">Capability targets are engineering decisions, not trophies.<\/p>\n<\/blockquote>\n\n\n\n<h2 class=\"wp-block-heading has-text-align-center\" style=\"font-size:32px\">Frequently Asked Questions<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\" style=\"font-size:22px\">What is a good Cpk value?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">For most manufacturing processes, a Cpk of 1.33 or higher is considered good \u2014 it is the widely accepted minimum for ongoing production. Critical or safety-related characteristics typically require 1.67 or higher, and 2.00 represents six sigma capability. A Cpk below 1.00 means the process is producing defects and needs immediate attention.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" style=\"font-size:22px\">Why is Cpk 1.33 the standard minimum instead of 1.00?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">A Cpk of 1.00 means the specification limit sits exactly three sigma from the mean \u2014 any shift in the process immediately produces defects. Cpk 1.33 adds a full sigma of buffer, so the process can absorb small, inevitable shifts before nonconforming parts appear.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" style=\"font-size:22px\">Why does PPAP ask for Ppk 1.67 instead of Cpk 1.67?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">At launch, a process has little history, so overall (long-term) variation is the more honest measure of what the customer will actually receive. Ppk uses overall standard deviation, making it the appropriate index for initial process approval before long-term stability has been demonstrated on a <a href=\"https:\/\/sigmadesk.app\/blog\/what-is-a-control-chart\/\">control chart<\/a>.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" style=\"font-size:22px\">Where does the 3.4 defects per million figure come from?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">It comes from combining a short-term six sigma process (Cpk = 2.00) with the assumed long-term 1.5 sigma shift of the mean. The shifted process is equivalent to a long-term Ppk of 1.50, which corresponds to about 3.4 defects per million opportunities.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" style=\"font-size:22px\">Is a higher Cpk always better?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Not economically. Beyond the level justified by the consequence of failure, additional capability costs money \u2014 tighter tolerances, better equipment, slower production \u2014 without a proportional reduction in real risk. Set the target based on what a defect would actually cost downstream.<\/p>\n\n\n\n<h2 class=\"wp-block-heading has-text-align-center\" style=\"font-size:32px\">Calculate Cpk and Ppk on Your Own Data<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">If you want to see where your own process stands, <a href=\"https:\/\/sigmadesk.app\/blog\/process-capability-calculator\/\">Cpk Calculator<\/a> is a <strong>free, web-based capability analysis module<\/strong> \u2014 no installation required. Paste in your data and instantly see Cp, Cpk, Pp, and Ppk, along with the expected defect rate your capability values imply.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>This article breaks down what each Cpk level really means in terms of sigma levels, defect rates, and practical risk, so you can set capability targets with confidence instead of habit. A Cpk of 1.33 is a four sigma process (\u2248 63 defective parts per million), a Cpk of 1.67 is a five sigma process [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_coblocks_attr":"","_coblocks_dimensions":"","_coblocks_responsive_height":"","_coblocks_accordion_ie_support":"","hide_page_title":"","footnotes":""},"categories":[1],"tags":[],"class_list":["post-389","post","type-post","status-publish","format-standard","hentry","category-educational"],"_links":{"self":[{"href":"https:\/\/sigmadesk.app\/blog\/wp-json\/wp\/v2\/posts\/389","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/sigmadesk.app\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/sigmadesk.app\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/sigmadesk.app\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/sigmadesk.app\/blog\/wp-json\/wp\/v2\/comments?post=389"}],"version-history":[{"count":5,"href":"https:\/\/sigmadesk.app\/blog\/wp-json\/wp\/v2\/posts\/389\/revisions"}],"predecessor-version":[{"id":424,"href":"https:\/\/sigmadesk.app\/blog\/wp-json\/wp\/v2\/posts\/389\/revisions\/424"}],"wp:attachment":[{"href":"https:\/\/sigmadesk.app\/blog\/wp-json\/wp\/v2\/media?parent=389"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/sigmadesk.app\/blog\/wp-json\/wp\/v2\/categories?post=389"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/sigmadesk.app\/blog\/wp-json\/wp\/v2\/tags?post=389"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}