{"id":294,"date":"2026-06-27T23:14:05","date_gmt":"2026-06-27T23:14:05","guid":{"rendered":"https:\/\/sigmadesk.app\/blog\/?page_id=294"},"modified":"2026-06-28T22:52:19","modified_gmt":"2026-06-28T22:52:19","slug":"process-capability-calculator","status":"publish","type":"page","link":"https:\/\/sigmadesk.app\/blog\/process-capability-calculator\/","title":{"rendered":"Process Capability Calculator (Cp, Cpk, Pp, Ppk)"},"content":{"rendered":"\n<h1 class=\"wp-block-heading has-text-align-center\" style=\"font-size:36px\">Process Capability &amp; Performance Calculator (Cp, Cpk, Pp, Ppk)<\/h1>\n\n\n\n<link rel=\"preconnect\" href=\"https:\/\/fonts.googleapis.com\">\n<link href=\"https:\/\/fonts.googleapis.com\/css2?family=Plus+Jakarta+Sans:wght@500;600;700;800&amp;display=swap\" rel=\"stylesheet\">\n\n<div id=\"sd-promo\" role=\"link\" tabindex=\"0\" aria-label=\"Open SigmaDesk and calculate your process capability\">\n\n  <style>\n    #sd-promo {\n      --sd-cyan: #06b6d4;\n      --sd-cyan-bright: #22d3ee;\n      --sd-blue: #2563eb;\n      --sd-purple: #a855f7;\n\n      font-family: 'Plus Jakarta Sans', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;\n      position: relative;\n      display: block;\n      width: 100%;\n      max-width: 1180px;\n      margin: 0 auto;\n      background: transparent;\n      cursor: pointer;\n      isolation: isolate;\n      -webkit-tap-highlight-color: transparent;\n    }\n    #sd-promo * { box-sizing: border-box; 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animation: none; }\n    }\n  <\/style>\n\n  <div class=\"sd-scroll-wrapper\" id=\"sd-scroll-wrapper\">\n    <div class=\"sd-inner\">\n      <img class=\"sd-img\" id=\"sd-img\" src=\"https:\/\/sigmadesk.app\/blog\/wp-content\/uploads\/2026\/06\/capability-1.png\" alt=\"SigmaDesk SPC platform \u2014 Capability analysis with Cp, Cpk, Pp, and Ppk indices\" loading=\"lazy\" decoding=\"async\" width=\"2045\" height=\"2009\">\n\n      <div class=\"sd-overlay\" aria-hidden=\"true\">\n        <div class=\"sd-card\">\n          <div class=\"sd-eyebrow\">SigmaDesk \u00b7 SPC Software<\/div>\n          <div class=\"sd-title\">Calculate your process capability<\/div>\n          <p class=\"sd-sub\">Paste your data and get instant Cp, Cpk, Pp, and Ppk \u2014 with a full capability report, histogram, and sigma rating in your browser.<\/p>\n          <span class=\"sd-btn\">Run your analysis free <span class=\"arr\">\u2192<\/span><\/span>\n        <\/div>\n      <\/div>\n    <\/div>\n\n    <div class=\"sd-badge\" aria-hidden=\"true\"><span class=\"dot\"><\/span> Calculate Cp &amp; Cpk free<\/div>\n  <\/div>\n\n<\/div>\n\n<script>\n(function () {\n  var SIGNUP_URL = \"https:\/\/sigmadesk.app\/auth\/register\";\n\n  var el = document.getElementById(\"sd-promo\");\n  var wrapper = document.getElementById(\"sd-scroll-wrapper\");\n  var img = document.getElementById(\"sd-img\");\n\n  var LARGE_SCREEN_BREAKPOINT = 1024;\n  var IMAGE_RATIO = 2009 \/ 2045;\n\n  function setHeight() {\n    var screenW = window.innerWidth;\n    var containerW = el.offsetWidth;\n\n    var effectiveW = screenW >= LARGE_SCREEN_BREAKPOINT\n      ? 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SIGMADESK Process Capability Calculator takes your measurement data and your specification limits and gives you the four indices that matter in industry \u2014 Cp, Cpk, Pp, and Ppk \u2014 calculated correctly, displayed clearly, and interpreted in context.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The four indices each serve a distinct purpose, and knowing which one to use is part of doing capability analysis right.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\" style=\"font-size:26px\"><strong>Cp<\/strong> &#8211; Potantial capability<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Cp measures the potential capability of the process: the ratio of the specification width to the natural process spread. It tells you whether the process could fit within spec if it were perfectly centered. It says nothing about where the process is actually located.<\/p>\n\n\n\n<div style=\"width:100%;height:280px;\"><canvas id=\"sd-cp\"><\/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<\/div>\n<p style=\"margin-top:10px;font-size:13px;font-family:system-ui,sans-serif;color:#888;font-style:italic;text-align:center;\">Cp = 1.67 \u2014 Centered process; the natural spread sits comfortably within both specification limits<\/p>\n<script>\n(function(){\n  function init(){\n    var LSL=49.5,USL=50.5,mu=50.0,sig=0.10,yMax=5.0;\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=49.0+2.0*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_cp',afterDraw:function(c){\n      var ctx=c.ctx,xs=c.scales.x,t=c.chartArea.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      ctx.restore();\n    }};\n    new Chart(document.getElementById('sd-cp'),{\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:49.0,max:51.0,ticks:{color:'#888',font:{size:11},stepSize:0.5,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<h2 class=\"wp-block-heading\" style=\"font-size:26px\">Cpk - Actual capability considering centering<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Cpk accounts for centering. It takes the minimum of the upper and lower capability ratios and reflects both spread and location. This is the index that tells you whether the process is actually performing within specification right now.<\/p>\n\n\n\n<div style=\"width:100%;height:280px;\"><canvas id=\"sd-cpk\"><\/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<\/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 = 0.67 \u2014 The same process spread, but the mean has drifted toward the lower specification limit<\/p>\n<script>\n(function(){\n  function init(){\n    var LSL=49.5,USL=50.5,mu=49.70,sig=0.10,yMax=5.0;\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=49.0+2.0*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_cpk',afterDraw:function(c){\n      var ctx=c.ctx,xs=c.scales.x,t=c.chartArea.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      ctx.restore();\n    }};\n    new Chart(document.getElementById('sd-cpk'),{\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:49.0,max:51.0,ticks:{color:'#888',font:{size:11},stepSize:0.5,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<h2 class=\"wp-block-heading\" style=\"font-size:26px\">Pp \u2013 Overall process performance<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Pp is the same concept as Cp but calculated using the overall standard deviation from all data points, rather than the within-subgroup estimate. Pp describes overall process performance as the data actually came out.<\/p>\n\n\n\n<div style=\"width:100%;height:280px;\"><canvas id=\"sd-pp\"><\/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<\/div>\n<p style=\"margin-top:10px;font-size:13px;font-family:system-ui,sans-serif;color:#888;font-style:italic;text-align:center;\">Pp = 1.11 \u2014 Centered, but the wider bell curve reflects all sources of variation across the full production run<\/p>\n<script>\n(function(){\n  function init(){\n    var LSL=49.5,USL=50.5,mu=50.0,sig=0.15,yMax=5.0;\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=49.0+2.0*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_pp',afterDraw:function(c){\n      var ctx=c.ctx,xs=c.scales.x,t=c.chartArea.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      ctx.restore();\n    }};\n    new Chart(document.getElementById('sd-pp'),{\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:49.0,max:51.0,ticks:{color:'#888',font:{size:11},stepSize:0.5,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<h2 class=\"wp-block-heading\" style=\"font-size:26px\">Ppk \u2013 Overall performance considering centering<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Ppk is the performance counterpart to Cpk. It combines overall spread with centering to reflect real-world process performance, including all sources of variation \u2014 shift-to-shift, operator-to-operator, lot-to-lot \u2014 that Cpk does not capture.<\/p>\n\n\n\n<div style=\"width:100%;height:280px;\"><canvas id=\"sd-ppk\"><\/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<\/div>\n<p style=\"margin-top:10px;font-size:13px;font-family:system-ui,sans-serif;color:#888;font-style:italic;text-align:center;\">Ppk = 0.44 \u2014 Off-center with wider overall spread; the lower tail visibly crosses the specification limit<\/p>\n<script>\n(function(){\n  function init(){\n    var LSL=49.5,USL=50.5,mu=49.70,sig=0.15,yMax=5.0;\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=49.0+2.0*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_ppk',afterDraw:function(c){\n      var ctx=c.ctx,xs=c.scales.x,t=c.chartArea.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      ctx.restore();\n    }};\n    new Chart(document.getElementById('sd-ppk'),{\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:49.0,max:51.0,ticks:{color:'#888',font:{size:11},stepSize:0.5,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\">The distinction between Cp and Cpk (short-term potential, using within-subgroup sigma) and Pp and Ppk (long-term performance, using overall sigma) is one of the most commonly misunderstood topics in Six Sigma training. SIGMADESK calculates and displays all four indices side by side so you can see both perspectives at once.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<p class=\"wp-block-paragraph\">Capability indices are only meaningful when they are calculated with the correct statistical method. SIGMADESK is built to match the formulas used in well known SPC software and taught in AIAG references.<\/p>\n\n\n\n<div class=\"wp-block-math\"><math display=\"block\"><semantics><mrow><msub><mi>C<\/mi><mi>p<\/mi><\/msub><mo>=<\/mo><mfrac><mrow><mi>U<\/mi><mi>S<\/mi><mi>L<\/mi><mo>\u2212<\/mo><mi>L<\/mi><mi>S<\/mi><mi>L<\/mi><\/mrow><mrow><mn>6<\/mn><msub><mi>\u03c3<\/mi><mrow><mi>w<\/mi><mi>i<\/mi><mi>t<\/mi><mi>h<\/mi><mi>i<\/mi><mi>n<\/mi><\/mrow><\/msub><\/mrow><\/mfrac><mo separator=\"true\">,<\/mo><msub><mi>C<\/mi><mrow><mi>p<\/mi><mi>k<\/mi><\/mrow><\/msub><mo>=<\/mo><mrow><mi>min<\/mi><mo>\u2061<\/mo><\/mrow><mrow><mo fence=\"true\" form=\"prefix\">(<\/mo><mfrac><mrow><mi>U<\/mi><mi>S<\/mi><mi>L<\/mi><mo>\u2212<\/mo><mover><mi>X<\/mi><mo stretchy=\"false\" class=\"tml-capshift\" style=\"math-style:normal;math-depth:0;\">\u203e<\/mo><\/mover><\/mrow><mrow><mn>3<\/mn><msub><mi>\u03c3<\/mi><mrow><mi>w<\/mi><mi>i<\/mi><mi>t<\/mi><mi>h<\/mi><mi>i<\/mi><mi>n<\/mi><\/mrow><\/msub><\/mrow><\/mfrac><mo separator=\"true\">,<\/mo><mfrac><mrow><mover><mi>X<\/mi><mo stretchy=\"false\" style=\"math-style:normal;math-depth:0;\">\u203e<\/mo><\/mover><mo>\u2212<\/mo><mi>L<\/mi><mi>S<\/mi><mi>L<\/mi><\/mrow><mrow><mn>3<\/mn><msub><mi>\u03c3<\/mi><mrow><mi>w<\/mi><mi>i<\/mi><mi>t<\/mi><mi>h<\/mi><mi>i<\/mi><mi>n<\/mi><\/mrow><\/msub><\/mrow><\/mfrac><mo fence=\"true\" form=\"postfix\">)<\/mo><\/mrow><\/mrow><annotation encoding=\"application\/x-tex\">C_p=\\frac{USL-LSL}{6\\sigma_{within}}\n,\nC_{pk}=\\min\\left(\n\\frac{USL-{\\bar{X}}}{3\\sigma_{within}},\n\\frac{\\bar{{X}}-LSL}{3\\sigma_{within}}\n\\right)<\/annotation><\/semantics><\/math><\/div>\n\n\n\n<p class=\"wp-block-paragraph\">Within-subgroup sigma and overall sigma are calculated and applied correctly. Cp and Cpk use the estimated within-subgroup standard deviation \u2014 derived from the average range or average standard deviation depending on your chart type \u2014 which reflects the process's short-term, inherent variation. Pp and Ppk use the sample standard deviation from all data pooled together. These are not the same number, and confusing them is one of the most common errors in spreadsheet-based capability work.<\/p>\n\n\n\n<div class=\"wp-block-math\"><math display=\"block\"><semantics><mrow><msub><mi>P<\/mi><mi>p<\/mi><\/msub><mo>=<\/mo><mfrac><mrow><mi>U<\/mi><mi>S<\/mi><mi>L<\/mi><mo>\u2212<\/mo><mi>L<\/mi><mi>S<\/mi><mi>L<\/mi><\/mrow><mrow><mn>6<\/mn><msub><mi>\u03c3<\/mi><mrow><mi>o<\/mi><mi>v<\/mi><mi>e<\/mi><mi>r<\/mi><mi>a<\/mi><mi>l<\/mi><mi>l<\/mi><\/mrow><\/msub><\/mrow><\/mfrac><mo separator=\"true\">,<\/mo><msub><mi>P<\/mi><mrow><mi>p<\/mi><mi>k<\/mi><\/mrow><\/msub><mo>=<\/mo><mrow><mi>min<\/mi><mo>\u2061<\/mo><\/mrow><mrow><mo fence=\"true\" form=\"prefix\">(<\/mo><mfrac><mrow><mi>U<\/mi><mi>S<\/mi><mi>L<\/mi><mo>\u2212<\/mo><mover><mi>X<\/mi><mo stretchy=\"false\" class=\"tml-capshift\" style=\"math-style:normal;math-depth:0;\">\u203e<\/mo><\/mover><\/mrow><mrow><mn>3<\/mn><msub><mi>\u03c3<\/mi><mrow><mi>o<\/mi><mi>v<\/mi><mi>e<\/mi><mi>r<\/mi><mi>a<\/mi><mi>l<\/mi><mi>l<\/mi><\/mrow><\/msub><\/mrow><\/mfrac><mo separator=\"true\">,<\/mo><mfrac><mrow><mover><mi>X<\/mi><mo stretchy=\"false\" style=\"math-style:normal;math-depth:0;\">\u203e<\/mo><\/mover><mo>\u2212<\/mo><mi>L<\/mi><mi>S<\/mi><mi>L<\/mi><\/mrow><mrow><mn>3<\/mn><msub><mi>\u03c3<\/mi><mrow><mi>o<\/mi><mi>v<\/mi><mi>e<\/mi><mi>r<\/mi><mi>a<\/mi><mi>l<\/mi><mi>l<\/mi><\/mrow><\/msub><\/mrow><\/mfrac><mo fence=\"true\" form=\"postfix\">)<\/mo><\/mrow><\/mrow><annotation encoding=\"application\/x-tex\">P_p=\\frac{USL-LSL}{6\\sigma_{overall}}\n,\nP_{pk}=\\min\\left(\n\\frac{USL-{\\bar{X}}}{3\\sigma_{overall}},\n\\frac{\\bar{{X}}-LSL}{3\\sigma_{overall}}\n\\right)<\/annotation><\/semantics><\/math><\/div>\n\n\n\n<p class=\"wp-block-paragraph\">A histogram with a fitted normal curve and specification limit overlays is generated automatically. This is not decoration \u2014 it is the visual check that tells you whether the normality assumption is reasonable, where the process is centered relative to spec, and how much of the tail is encroaching on the boundary.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Capability ratings give you immediate context for every index. Rather than leaving you to interpret a raw number against a memorized benchmark, SIGMADESK applies a five-tier rating system \u2014 from Incapable through World Class \u2014 so you see not just the number but what it means for your process.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Specification limits are yours to define. One-sided specs, bilateral specs, or a target with only an upper or lower limit \u2014 the calculator handles all configurations without forcing a two-sided format on every situation.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" style=\"font-size:1px\">More on Statistical Process Control<\/h2>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\" style=\"font-size:30px\">More on Statistical Process Control<\/h2>\n\n\n\n<div class=\"wp-block-query is-layout-flow wp-block-query-is-layout-flow\"><ul class=\"wp-block-post-template is-layout-flow wp-block-post-template-is-layout-flow\"><li class=\"wp-block-post post-345 post type-post status-publish format-standard hentry category-educational\">\n<h2 class=\"wp-block-post-title\"><a href=\"https:\/\/sigmadesk.app\/blog\/cp-and-cpk-difference\/\" target=\"_self\" >Cp and Cpk: What&#8217;s the Difference? Explained<\/a><\/h2>\n\n\n\n<div style=\"padding-top:0;padding-bottom:0\" class=\"wp-block-post-excerpt has-small-font-size\"><p class=\"wp-block-post-excerpt__excerpt\">Process capability indices, Cp and Cpk, are two of the most commonly reported numbers in quality engineering. They&#8217;re calculated from the same underlying measurement data but they answer two different questions, and confusing them can lead to the wrong conclusion about whether a process is actually capable. This article focuses specifically on the distinction between Cp and Cpk, so if you need a fuller introduction and more comprehensive look to the process capability, that&#8217;s better you start with complete guide on Process Capability. Here, the goal is to make the difference between these two indices unambiguous. What Cp Measures Cp&hellip; <\/p><\/div>\n\n\n<hr class=\"wp-block-separator has-css-opacity\"\/>\n\n\n<div class=\"wp-block-post-date\"><time datetime=\"2026-06-30T11:17:21+00:00\">June 30, 2026<\/time><\/div>\n<\/li><li class=\"wp-block-post post-122 post type-post status-publish format-standard hentry category-educational\">\n<h2 class=\"wp-block-post-title\"><a href=\"https:\/\/sigmadesk.app\/blog\/standard-deviation\/\" target=\"_self\" >Population vs. Sample Standard Deviation: What&#8217;s the Difference?<\/a><\/h2>\n\n\n\n<div style=\"padding-top:0;padding-bottom:0\" class=\"wp-block-post-excerpt has-small-font-size\"><p class=\"wp-block-post-excerpt__excerpt\">A practical guide to standard deviation \u2014 what it measures, why it matters, and the difference between population and sample standard deviation explained with clear examples. Standard deviation is one of the most important concepts in statistics. It appears in manufacturing quality control, finance, healthcare, scientific research, and virtually any field where data needs to be understood. Yet despite its widespread use, the concept is often explained in ways that feel abstract or overly mathematical. This guide breaks it down step by step \u2014 what standard deviation actually measures, how to calculate it, and why there are two different versions&hellip; <\/p><\/div>\n\n\n<hr class=\"wp-block-separator has-css-opacity\"\/>\n\n\n<div class=\"wp-block-post-date\"><time datetime=\"2026-06-29T23:36:11+00:00\">June 29, 2026<\/time><\/div>\n<\/li><li class=\"wp-block-post post-29 post type-post status-publish format-standard hentry category-educational\">\n<h2 class=\"wp-block-post-title\"><a href=\"https:\/\/sigmadesk.app\/blog\/what-is-a-control-chart\/\" target=\"_self\" >SPC Control Charts for Variables (I-MR, Xbar-R, Xbar-S) Explained<\/a><\/h2>\n\n\n\n<div style=\"padding-top:0;padding-bottom:0\" class=\"wp-block-post-excerpt has-small-font-size\"><p class=\"wp-block-post-excerpt__excerpt\">A practical guide to control charts \u2014 from common vs. special cause variation to I-MR, X\u0304-R and X\u0304-S charts, control limit formulas, and when to use each one. Control charts are one of the core tools used in&nbsp;Six Sigma, quality management, and process improvement methodologies. They are especially common in engineering and manufacturing, but their usefulness is not limited to these fields. In fact, control charts can be applied anywhere data is collected over time. For example, you might use a control chart when you are: Although these examples come from different areas, they all have one important thing in&hellip; <\/p><\/div>\n\n\n<hr class=\"wp-block-separator has-css-opacity\"\/>\n\n\n<div class=\"wp-block-post-date\"><time datetime=\"2026-06-28T19:01:48+00:00\">June 28, 2026<\/time><\/div>\n<\/li><\/ul><\/div>\n","protected":false},"excerpt":{"rendered":"<p>Process Capability &amp; Performance Calculator (Cp, Cpk, Pp, Ppk) SigmaDesk \u00b7 SPC Software Calculate your process capability Paste your data and get instant Cp, Cpk, Pp, and Ppk \u2014 with a full capability report, histogram, and sigma rating in your browser. Run your analysis free \u2192 Calculate Cp &amp; Cpk free Built for Real Capability [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_coblocks_attr":"","_coblocks_dimensions":"","_coblocks_responsive_height":"","_coblocks_accordion_ie_support":"","hide_page_title":"enabled","footnotes":""},"class_list":["post-294","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/sigmadesk.app\/blog\/wp-json\/wp\/v2\/pages\/294","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/sigmadesk.app\/blog\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/sigmadesk.app\/blog\/wp-json\/wp\/v2\/types\/page"}],"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=294"}],"version-history":[{"count":8,"href":"https:\/\/sigmadesk.app\/blog\/wp-json\/wp\/v2\/pages\/294\/revisions"}],"predecessor-version":[{"id":342,"href":"https:\/\/sigmadesk.app\/blog\/wp-json\/wp\/v2\/pages\/294\/revisions\/342"}],"wp:attachment":[{"href":"https:\/\/sigmadesk.app\/blog\/wp-json\/wp\/v2\/media?parent=294"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}