Quality Control Tool
AQL Calculator
AQL (Acceptable Quality Limit) is the worst defect rate you are still willing to accept in a lot. This calculator turns that target into a sampling plan: how many units to inspect from a production lot, and how many can fail before the lot is rejected. Enter the lot size, confidence target, defect rate to rule out, and allowed defect count to build a practical incoming inspection plan.
Units to inspect
ACCEPT on 0 defects
Inspect 381 of 1,200. If none fail, you are 99% confident the lot defect rate is below 1%.
This calculator estimates a lot-screening plan. It does not replace ANSI/ASQ Z1.4, customer plans, or C=0 Squeglia table lookups.
| Defect threshold (D) | 12 units or more |
|---|---|
| Infinite-lot sample size | 459 |
| Actual confidence at sample size | 99.005% |
| Sample share of lot | 31.8% |
How to use this AQL sampling calculator
AQL sampling checks a representative subset of a lot instead of inspecting every unit. Choose a stricter confidence level or lower defect rate when failures are costly, and use customer requirements or ANSI/ASQ Z1.4 when a formal inspection standard is required.
This AQL calculator online starts with four inputs: lot size, confidence target, defect rate to catch, and allowed defects. The result is a practical sampling plan: how many units to draw, how many failures can still pass the lot, and what confidence the plan actually reaches after finite-lot math is applied. It is most useful for production lots, receiving checks, and pre-shipment inspection where testing every unit would cost too much time, consume destructive samples, or slow a build that otherwise looks controlled.
What AQL sampling means
Acceptable Quality Limit is a way to define how much lot-level risk you are willing to tolerate. In plain terms, you are asking, “If this lot were actually at a bad defect rate, how many pieces would I need to inspect before I would probably catch it?” For cable assemblies and wire harnesses, the checked defect might be a missing crimp, wrong pinout, continuity failure, label mismatch, or workmanship issue found during incoming inspection. The calculator does not decide what is acceptable for your product; it turns that risk target into a draw size you can put on an inspection traveler.
Worked example: 1,200-piece harness lot
Suppose a production run has 1,200 units and you want to catch a lot that is 1% defective. Set lot size to 1,200, defect rate to catch to 1%, confidence target to 99%, and allowed defects to 0. The calculator returns 381 units to inspect. It also shows a defect threshold of 12 units, meaning the plan is designed around a lot that contains 12 or more bad pieces. If none of the 381 inspected units fail, the lot passes this screening rule and the actual confidence is just over 99%. If even one unit fails with allowed defects set to 0, the lot should be held for disposition, rework, or a tighter customer-defined plan.
ANSI/ASQ Z1.4 or custom AQL?
Use ANSI/ASQ Z1.4 when a customer contract, regulated quality system, or supplier quality agreement calls for a recognized sampling standard. Z1.4 gives you inspection levels, code letters, normal/tightened/reduced switching rules, and accept/reject numbers that are easier for buyers and auditors to recognize.
Use a custom AQL calculation when you need a quick engineering estimate, a documented internal screen, or a way to compare inspection burden before placing an order. For example, a prototype build may only need a practical receiving check, while a recurring assembly may deserve a customer-approved plan tied to the drawing, test procedure, and production quote.
AQL FAQ
What sample size do I need for a 500-unit lot at 1% AQL?
With this calculator set to 99% confidence and zero allowed defects, a 500-unit lot at a 1% defect rate returns a 300-unit sample. If you allow one defect or choose a lower confidence target, the result changes.
What is the difference between AQL and Cpk?
AQL is lot acceptance sampling: it helps decide how many finished units to inspect. Cpk is process capability: it measures whether a stable process can stay inside specification limits. Use Cpk to manage the process and AQL to screen lots.
Does passing an AQL plan prove the lot has no defects?
No. Passing means the sample did not find enough defects to reject the lot under the selected rule. It reduces risk; it does not make the lot defect-free.
Should destructive tests use the same sample size?
Usually not. If inspection destroys the part, combine smaller destructive samples with process controls such as setup verification, pull testing, crimp-height checks, and first-article review.