p Chart Formulas

The p Chart is used to evaluate process stability when counting the number or fraction defective.

The p Chart is used when the sample size varies. Examples include the number of defective products, meals in a restaurant, incorrect prescriptions, bills, invoices, paychecks, etc.

Here is the formula used to calculate a p Chart.

p chart formula

pᵢ = number of non-conforming items
nᵢ = sample size

Conforms with ANSI/ASQC B1, B2, B3 1996


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The p Chart is just one of the tools included in QI Macros SPC Software for Excel.


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