Sample Size and Confidence Calculator

Study Sample Size Planner

Choose whether you are sizing for measured data or attribute data, then set the margin of error, confidence level, and variation estimate.

Variable data: n = (z x sigma / E)^2
Attribute data: n = z^2 x p(1-p) / E^2

Planner mode Variable data for capability studies, audits, and dimensional checks Attribute data for pass/fail, defect-rate, and audit-conformance checks

Use case preset Confidence level Desired margin of error Process variation estimate (sigma) Estimated defect rate p (0 to 1, attribute mode) Population size (optional finite population correction)

Planning Notes

The calculator returns the minimum whole-number sample size needed for the confidence target you selected.

Use a stronger sigma estimate or tighter error band when a study will drive customer-critical or release decisions.

If you apply population correction, the result shrinks only when the population is relatively small compared with the sample.

AQL-Based Incoming Quality Planner

Build a practical incoming inspection sample plan from lot size, inspection level, and AQL target. This module gives a planning estimate inspired by standard acceptance-sampling logic.

Approximation: Ac from Poisson expectation at AQL
Planning note: Verify contractual plans against official ANSI/ASQ tables

Lot size Inspection level AQL (%) Expected incoming defect rate (%)

Acceptance Sampling Notes

Use this for planning and supplier discussions, then confirm any released inspection plan against the official standard your customer requires.

Higher inspection levels drive larger samples and tighter screening; lower AQL values do the same.

If the expected incoming defect rate is higher than the AQL, the acceptance probability falls and supplier containment becomes more urgent.

How to Use This App

For a capability study or variable inspection, enter your best estimate of process variation, set the error band you can tolerate, and choose the confidence level your decision requires. The app returns the minimum recommended sample size, plus a finite-population adjustment when the total population is limited.

For attribute studies such as conformance audits or defect-rate checks, switch to attribute mode and enter an estimated defect proportion. If you do not have historical data, start with a conservative estimate and then refine your plan after the first collection cycle.

The AQL section is useful for incoming inspection planning. Enter lot size, select the general inspection level, and choose the AQL target. The app estimates a code letter, sample size, and acceptance number so you can discuss the plan with suppliers or your quality team.

For customer-specific, regulated, or contractual sampling requirements, validate the plan against the exact published standard and any site procedures before release.