Within and Overall Process Capability

How to use Within and Overall Process Capability

Within-subgroup variance pools centered subgroup squared deviations over their combined sample degrees of freedom. Overall variance uses all observations about their overall mean. Cp/Cpk use the within estimate; Pp/Ppk use the overall estimate, and centering distances are calculated after an origin shift.

1. Enter subgroup measurement matrix json, lower specification limit, upper specification limit.
2. Choose the stated convention and check the units and supported model.
3. Calculate, inspect the result, then copy or download it.

Good to know

• 2–100 rationally selected subgroups of 2–50 observations; at most 1000 total. Finite numeric magnitudes are at most 1e9 and nonzero magnitudes at least 1e-12. Both variation estimates must be positive; specification limits must increase. No bias correction, confidence interval, defect-rate prediction or pass/fail threshold. Stable approximately normal independent data and meaningful subgroup design are assumptions, not verified conclusions. Small samples can make indices unreliable.
• Local calculation only; no input persistence or external lookup. Text/JSON is limited to 30000 characters and output to 1000000 characters. Numeric model inputs and precision/work limits are stated on this page. Approximate JSON numbers retain full stored values; exact arithmetic outputs retain decimal or fraction strings. Unsupported states fail explicitly.