How do you calculate a sampling plan size?

Multiply the lot size by the sampling rate, then take whichever is larger between that result and your minimum sample size. A 2000-part lot at 10% gives 200, which beats the 50-part floor.

What is a good sampling rate?

It depends on risk and history. 10% is a common general rule, but critical characteristics or unproven suppliers warrant higher rates, while a long history of clean lots can justify reduced sampling.

Why have a minimum sample size?

On small lots a flat percentage can pull just a handful of parts, which gives almost no confidence. A floor like 50 ensures even a small lot gets enough inspection to catch a problem.

Is percentage sampling the same as AQL sampling?

No. Percentage sampling is simple but not statistically rigorous; the same defect rate gives different consumer risk at different lot sizes. AQL plans like Z1.4 set sample size and accept numbers to a defined risk and are required for many contracts.

How do I decide accept or reject after sampling?

This tool sizes the sample only. You still need an acceptance number; for a percentage plan many shops accept on zero defects, but for a formal plan use the accept/reject criteria that come with the AQL table.

Does a bigger lot always mean a bigger sample?

Under percentage sampling, yes, the sample grows with the lot, which is one reason it differs from AQL plans where sample size grows much more slowly than lot size.

Quality & Metrology calculator

Sampling Plan Size Calculator

Sampling plan size is the number of parts you pull from a production lot for inspection, set by applying a sampling rate to the lot and never dropping below an agreed minimum. Quality engineers, incoming inspectors, and metrology teams use it to balance inspection cost against the risk of accepting a bad lot. This calculator takes your lot size and percentage sampling rate, then enforces a minimum sample floor so small lots still get meaningful coverage. Getting the sample size right is what makes an acceptance decision defensible, because too few parts and a defective lot slips through, while too many wastes inspection labor and gate time.

What this calculator does

Estimate sample size for a lot from the lot size, a percentage sampling rate, and a minimum sample required by your plan.
Use it when planning inspection workload and you need to know how many samples a lot will require.
It multiplies lot size by sampling rate, then takes the larger of that and your minimum sample size as the required sample.

Formula used

Calculated sample = lot size × sampling rate
Required sample size = max(calculated sample, minimum sample size)

Inputs explained

Lot size: Enter the number of parts in the lot or shipment to be sampled.
Sampling rate: Use the percentage sampling rate from your inspection plan or control plan.
Minimum sample size: Enter the minimum sample required by the customer, standard, or internal policy.

How to use the result

Use it to set incoming, in-process, or final inspection sample sizes when you sample by a fixed percentage with a floor.
A flat percentage rule is not statistically equivalent to a standard AQL plan; for contractual acceptance sampling, derive sample size and accept/reject numbers from ANSI/ASQ Z1.4 or similar.

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 a sampling plan size? Multiply the lot size by the sampling rate, then take whichever is larger between that result and your minimum sample size. A 2000-part lot at 10% gives 200, which beats the 50-part floor.
What is a good sampling rate? It depends on risk and history. 10% is a common general rule, but critical characteristics or unproven suppliers warrant higher rates, while a long history of clean lots can justify reduced sampling.
Why have a minimum sample size? On small lots a flat percentage can pull just a handful of parts, which gives almost no confidence. A floor like 50 ensures even a small lot gets enough inspection to catch a problem.
Is percentage sampling the same as AQL sampling? No. Percentage sampling is simple but not statistically rigorous; the same defect rate gives different consumer risk at different lot sizes. AQL plans like Z1.4 set sample size and accept numbers to a defined risk and are required for many contracts.
How do I decide accept or reject after sampling? This tool sizes the sample only. You still need an acceptance number; for a percentage plan many shops accept on zero defects, but for a formal plan use the accept/reject criteria that come with the AQL table.

Last reviewed 2026-05-12.