ANSI/ASQ Z1.4 AQL Chart & Lookup Tables

This is a AQL Chart lookup page for all product inspection services, not a tutorial and not a calculator. It contains the tables inspectors work from on site: the sample size code letter table, and the single sampling Ac/Re matrices for all three quality inspection severities — normal, tightened and reduced — at general levels I, II and III. If you want the reasoning behind the standard, read our ANSI/ASQ Z1.4 sampling guide. If you want the numbers computed for you, use the AQL sampling calculator.

Most published AQL charts stop at normal inspection. This one carries all three severities, because the tightened and reduced schedules turned out to be genuinely hard to find elsewhere — see why we built this page.

What this page adds that the other two do not is the part that most AQL charts leave out: the conditions under which the number you looked up stops being valid. An Ac/Re pair is only meaningful if the lot was formed correctly, the product inspection is at normal severity, the sampling is single rather than double, and the arrows were followed. The sections below cover each of those.

Table A — Sample Size Code Letters (ANSI/ASQ Z1.4 Table I)

Column II (highlighted) is the default general inspection level for most pre-shipment inspections. Special levels S-1 to S-4 are reserved for destructive or high-cost tests.

Table B — Single Sampling Plans for Normal Inspection

A cell reading ↓ 1 / 2 means: use the first sampling plan below the arrow — sample size and Ac/Re as shown. A cell reading ↑ 21 / 22 means: use the first plan above. Never use the numbers sitting next to the arrow.

Switching Rules: Normal, Tightened and Reduced

Severity is not a column you choose. ANSI/ASQ Z1.4 starts every new product or supplier at normal quality inspection, and then moves you between three severities according to how the recent lots actually performed. The move is triggered by the results, not agreed between the parties — once the condition is met, the next lot is inspected under the new severity.

• Normal — the default starting point. Table B above.
• Tightened — a lower acceptance number at broadly the same sample size. Table C below.
• Reduced — a smaller sample, and a deliberate gap between Ac and Re. Table D below.

Where this goes wrong in practice. The rule that catches importers out is the return from reduced to normal. A single rejected lot ends reduced inspection at once, and so does irregular production — but the trigger lives on the inspection record, not in anyone's inbox. We have seen suppliers stay on reduced severity for months after the condition that justified it had expired, simply because nobody was keeping the running sequence of lot results. These switching rules are only enforceable if somebody is keeping that record.

Table C — Single Sampling Plans for Tightened Inspection

Tightened inspection keeps the sample size a normal plan would use for that code letter but lowers the acceptance number: code K at AQL 2.5 moves from Ac 7 / Re 8 under normal to Ac 5 / Re 6 under tightened. Arrow rules are identical to Table B — see Arrow Rules.

Worked example. Lot of 3,000 units, General Inspection Level II, AQL 0.4 under tightened inspection. Table A gives code letter K (sample 125), but the K cell here carries ↓. Follow it down to code L: you must draw 200 units, not 125, against Ac 1 / Re 2. Reading 125 against a 0.4 AQL is not a Z1.4 tightened plan at all.

Table D — Single Sampling Plans for Reduced Inspection

Reduced inspection draws a smaller sample for the same code letter — that reduction is the point of reduced inspection, not a rounding difference, so the same letter does not mean the same quantity in all three tables. It also leaves a gap between Ac and Re in most cells: a result above Ac but below Re is marked ^†, meaning the lot is accepted but the next lot returns to normal inspection. Cells showing Re = Ac + 1 carry no dagger, because there is no middle result to decide.

Before You Look Up a Number: Five Checks

Run through these before reading a cell off the matrix. If any one fails, the Ac/Re pair is not describing your product inspection.

1. This is single sampling, attribute inspection. One sample is drawn once, and each unit is judged conforming or non-conforming. It is not a double or multiple sampling plan, and it is not variables inspection.
2. You know which severity you are in. Tightened and reduced severity are separate tables reached through switching rules, never by choosing a different column here.
3. Your lot is homogeneous. See Lot formation below — this is the check that fails most often.
4. The inspection unit is defined. A unit is one item as sold (one shoe, not one pair; one retail carton, not one master carton). Changing the unit changes the lot size and therefore the code letter.
5. Critical, Major and Minor are three separate lookups. Each class carries its own AQL and must be read from this table separately, with its own pass/fail decision. You cannot offset Major defects with zero Minor defects, and you cannot add the classes together to reach a single acceptance number.

Arrow Rules: The Table Is Redirecting You

An arrow is not decoration and not an error. It means this combination of code letter and AQL has no sampling plan of its own, and the standard is directing you to the nearest plan that does.

• ↓ — use the first sampling plan below the arrow. You move to a larger sample size.
• ↑ — use the first sampling plan above the arrow. You move to a smaller sample size.
• The Ac/Re shown next to the arrow in the table above is the plan you end up using — after the jump, not at the cell you started from.

Worked example. Lot of 3,000 units, General Inspection Level II. Table A puts 1,201–3,200 at Level II on code letter K (sample 125). If your AQL is 2.5, the K row gives Ac 7 / Re 8 with no arrow — inspect 125 units. But if your AQL is 0.25, the cell carries ↓: code K has no plan at that AQL, and you must follow the arrow down to code L, sample 200, Ac 1 / Re 2. Reading 125 units against a 0.25 AQL would not be a Z1.4 plan at all.

Ignoring the arrow and using whatever number sits nearest is one of the most common and least visible errors in this industry, because the quality control inspection still looks legitimate on the report. This is also why two parties can quote the same AQL and arrive at different sample sizes — one followed the arrow, the other did not.

Limits of These Tables

• Sample size exceeds lot size (n > N). When the plan calls for as many units as the lot contains, or more, the requirement is 100% inspection of the lot — not a partial sample. This typically appears with very small lots at high general levels. At that point you have left AQL sampling; see 100% full inspection.
• AQL is not a defect-rate guarantee. It is the process average the plan is built around, not a ceiling on what ships. A plan can meet AQL 2.5 and still accept lots well above 2.5% defective.
• AQL is not LTPD. This table does not show the Lot Tolerance Percent Defective, so it does not tell you how well the plan rejects genuinely bad lots. If your contract requires protection above a specific LTPD, Z1.4 single sampling may not be sufficient on its own. OC curves and producer/consumer risk for these plans are covered in the AQL calculator.
• General levels only. Special levels S-1 to S-4 are not shown here; they apply to destructive or high-cost tests and are handled in the calculator.
• Not for rectifying inspection. These tables judge a lot; they do not describe the quality of goods that leave after 100% sorting and rework.

Lot Formation: When One Lot Is Really Three

The validity of any number in these tables depends on the lot being formed correctly. Z1.4 assumes units of the same type, grade, size and composition, produced under essentially the same conditions and at essentially the same time. If that assumption is broken, the sample no longer represents a single population and the Ac/Re values lose their statistical meaning — even if every lookup step was performed correctly.

Groupings that invalidate the plan:

• Mixing different SKUs, mould runs, production dates or suppliers into one lot.
• Consolidating partial shipments from separate production batches into a single inspection lot.
• Splitting one continuous run into several lots purely to obtain a smaller sample size.

Where a lot contains clear sub-lots — different production days, shifts or lines — samples should be allocated across those sub-lots in proportion to their size rather than drawn at random from the whole. As a practical test: if your 5,000 units were produced over four days, four separate lookups against the four day-quantities will usually tell you more than one lookup against 5,000. Where your inspection specification needs custom lotting rules, that belongs in the QC agreement before order confirmation, not in a conversation after the goods are made.

Drawing the Sample: Random Does Not Mean Convenient

These tables tell you how many units to inspect. They do not tell you which units — and on a factory floor, that is where a plan quietly fails.

• Top-of-stack bias. Cartons have to come from different layers of the pallet, not from the top layer that happens to be easiest to reach.
• Placed units. Known-good cartons are sometimes positioned near the aisle or at the front of a stack. Our inspectors walk the full storage area and pull from the back rows.
• Warehouse vs. production line. Sampling packed cartons out of finished goods is not the same as pulling units off a running line. How the sample is spread across the lot changes with how homogeneous the goods actually are.

A sample drawn for convenience is not a random sample, and no table corrects for it afterwards.

Re-inspection and Re-submitted Lots

This normal inspection table applies to the original inspection of a lot. Z1.4 does not grant an automatic second chance: a lot that has failed, been reworked or been sorted does not simply re-enter the same plan.

Your purchase contract needs to state explicitly:

• whether re-inspection uses the same inspection level;
• whether tightened severity is triggered automatically after a failure;
• whether units previously rejected are excluded from the re-submitted lot.

Most disputes in this area arise because a factory assumes a failed lot can be re-submitted to the identical lookup plan, and the buyer assumes otherwise. Neither assumption is in the standard — it has to be written into the order.

Scope of This Chart

These tables are for attribute inspection of general consumer goods. Medical devices, automotive, aerospace and regulated electronics are frequently governed by modified or industry-specific sampling standards, and Z1.4 should not be assumed to apply. Where goods are high-risk or regulated, the applicable standard should be confirmed before product inspection rather than inferred from a general-purpose AQL table.

Why This AQL Chart Page Exists

This page started with a phone call from Berlin on 13 October 2026. A German client was preparing a quality workshop with his rubber boot manufacturer in Taizhou, Jiangsu. His plan was to phase quality assurance inspection tighter over time — moving from reduced to normal to tightened sampling as the factory improved toward his target specification.

He could not find the tightened or reduced schedules anywhere. Every free AQL resource he searched covered normal inspection only. He then checked with colleagues and supply chain peers — but they came up empty as well. He reached out to us, said that we were professional third-party inspection company, which is his last hope for accessing the complete standard tables.

We sent him the documents, then ran the same search ourselves. He was right — even our own AQL calculator only implements normal single sampling.

If quality professionals and importers genuinely need the complete set — whether for quality ramp-up, or for stable, low-risk inspection programs, it should not be this hard to find. So we published this full ANSI/ASQ Z1.4 (and its predecessor MIL-STD-105E) single-sampling chart, covering normal, tightened, and reduced plans in one place.