Cpk and Ppk calculator

Cp/Cpk use within-subgroup sigma (short-term). Pp/Ppk use the overall sample standard deviation (long-term). Leave one limit blank for a one-sided spec.

Which number should I report?

Cpk shows what the process could do if it stays stable; Ppk shows what it actually did across the data. A large gap usually means shifts or drift between subgroups. Read the Cpk vs Ppk guide. Already know your mean and σ? Use the process capability calculator.