How do you calculate Ppk?

Take the distance from the mean to the nearest spec limit, subtract any required clearance buffer, then divide by the one-sided three-sigma spread. Here (0.40 - 0.04) / 0.30 = 0.36 / 0.30 = 1.20.

What is a good Ppk value?

1.33 is the standard minimum for a qualified process and 1.67 is expected for critical or safety characteristics. The example's 1.20 is below the usual floor and would typically trigger a corrective action.

What is the difference between Pp and Ppk?

Pp assumes perfect centering and only measures spread; Ppk uses the nearest limit and therefore drops as the process moves off-target. Ppk is always less than or equal to Pp.

What does a Ppk of 1.20 mean?

It means the nearest spec limit sits 3.6 standard deviations from the mean (1.20 x 3), corresponding to roughly 159 defective parts per million on that tail — usable but not yet at the 1.33 target.

Is Ppk or Cpk more important?

Cpk reflects short-term potential; Ppk reflects what actually shipped over the long run. Customers care most about Ppk because it includes all real-world variation and drift.

Yes. If the process mean falls outside the nearest spec limit, the effective distance goes negative and Ppk becomes negative, signaling the average part is already out of spec.

Quality & Metrology calculator

Ppk Calculator

Ppk is the centering-aware long-term capability index: it measures the distance from the process mean to the nearest specification limit in units of three standard deviations, so it penalizes a process for both excess variation and being off-target. Quality engineers rely on Ppk over Pp because a real process is rarely perfectly centered, and it is the number most customers write into their PPAP and supplier scorecards. A Ppk of 1.33 corresponds to roughly 32 defective parts per million on the worst-case tail; 1.67 corresponds to a few PPM. When Ppk is well below Pp, the message is unambiguous: the spread is fine, but the mean needs to be shifted toward the center of the tolerance.

What this calculator does

Estimate process performance Ppk as the distance from the process mean to the nearest specification limit, divided by the one-sided long-term spread.
Use it when reporting overall, long-term performance of an off-center feature for a PPAP or capability submission.
It divides the effective distance from the process mean to its nearest spec limit (after subtracting any required clearance buffer) by the one-sided long-term three-sigma spread.

Formula used

Adjusted distance to limit = distance to nearest spec limit − required clearance buffer
Ppk = adjusted distance to limit ÷ one-sided long-term spread (3 sigma)

Inputs explained

Distance from mean to nearest spec limit:
Required clearance buffer:
One-sided long-term spread (3 sigma):

How to use the result

Use it as your headline long-term capability number on capability studies, PPAP submissions, and control-plan reviews where centering matters.
Ppk only reflects the nearest limit, so a badly skewed or bimodal distribution can post an acceptable Ppk while still producing defects at the far tail; verify the assumption of normality.

Current U.S. benchmarks

U.S. manufacturing runs at 75.6% of capacity (Federal Reserve, May 2026). New factory orders are up 2.3% year over year (Census).

Common questions

How do you calculate Ppk? Take the distance from the mean to the nearest spec limit, subtract any required clearance buffer, then divide by the one-sided three-sigma spread. Here (0.40 - 0.04) / 0.30 = 0.36 / 0.30 = 1.20.
What is a good Ppk value? 1.33 is the standard minimum for a qualified process and 1.67 is expected for critical or safety characteristics. The example's 1.20 is below the usual floor and would typically trigger a corrective action.
What is the difference between Pp and Ppk? Pp assumes perfect centering and only measures spread; Ppk uses the nearest limit and therefore drops as the process moves off-target. Ppk is always less than or equal to Pp.
What does a Ppk of 1.20 mean? It means the nearest spec limit sits 3.6 standard deviations from the mean (1.20 x 3), corresponding to roughly 159 defective parts per million on that tail — usable but not yet at the 1.33 target.
Is Ppk or Cpk more important? Cpk reflects short-term potential; Ppk reflects what actually shipped over the long run. Customers care most about Ppk because it includes all real-world variation and drift.

Last reviewed 2026-05-12.