Control Chart Calculation Formula

Standard Deviation Calculation

P chart:

  •  P= percent or rate
  •  N= number of trails












C chart:

  • X= the average

Upper and Lower Limit Calculation

X-bar Chart
  • Lower Control Limit = (Mean – 3×sigma) ÷ n(1/2)
  • Center Line = Process mean
  • Upper Control Limit = (Mean + 3×sigma) ÷ n(1/2)


R-bar chart

  • Lower Control Limit = R-bar – 3×d3×sigma
  • Center Line = R-bar
  • Upper Control Limit = R-Bar + 3×d3×sigma


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