Fabric 4-Point Inspection and AQL Calculator

The 4-point system is the fabric-specific version of quality inspection: instead of counting defects across an area, an inspector counts points against a roll length table, and the total decides the roll. This calculator gives the sample size and the acceptance number for a given AQL and inspection level, so a purchase order can specify the inspection in numbers rather than in words.

Why Fabric Uses a Different System

Garment inspection counts defects against a table of acceptable points per garment. Fabric cannot be inspected that way, because a 6,000 metre roll is not a countable number of units. The 4-point system solves this by scoring each defect by its length and counting points rather than pieces.

Under the 4-point system each defect is worth points according to how large it is. The standard scale is:

Two numbers need separating. The acceptance number is not a calculation you do yourself: it comes from a standard table, read across from your AQL and down from your code letter, and it is the count of defects at which the lot still passes. ISO 2859-1 gives it for every combination, and this calculator reads it from that table rather than estimating it. The total number of points you are allowed across the sample is a different figure: that is your inspection density multiplied by the sample size, and it tells you how much room you have before the roll is in trouble.

Inspection points are usually written as 100 points per square yard. This calculator works in points per square metre, so divide a per-square-yard figure by 1.196 to convert it. The unit matters more than it looks: at a 2,000 m sample the difference between the two conventions is around two hundred points, which is often the difference between passing and failing a roll.

Sample Size Comes From the Lot, Not From Your Preference

Sample size is set by the lot size and the inspection level, and the level is where the commercial negotiating happens. General inspection level II is the default and what most purchase orders mean when they say nothing. Level I is tightened and is justified only where defects genuinely threaten the product. Level III is reduced and exists for large lots where the risk is proportionally smaller.

Level I does not mean more careful inspectors on the same sample. It means a smaller effective lot, which pushes the lot into a smaller code letter, which means a larger sample. Tightening the level therefore increases inspection cost directly, and it is worth pushing back on a level I requirement if the defects would not actually cause a claim.

Writing the Inspection Into the Purchase Order

The value of putting numbers in the contract is that the inspection becomes a measurement rather than an opinion. A usable clause specifies the standard, the inspection level, the AQL, the sample size, and who bears the cost of a failed lot. Missing any one of these is where disputes come from.

A typical clause reads: inspection under ASTM D5430 four-point system, general inspection level II, AQL 2.5, sample size as determined by lot quantity, and the inspection cost borne by the seller if the lot fails on first inspection. The last part matters commercially: without it, a failed lot means inspection twice, and the cost of the second inspection is usually negotiated awkwardly.

Where 4-Point Differs from 10-Point

The 10-point system, used in Europe, counts every defect as one point regardless of size. It is more punitive and cannot be aggregated by size, which makes it less informative on a fabric roll where most defects are small. If a buyer’s QC team is trained on 10-point and the contract is silent, the two teams will produce different acceptances on the same fabric. Specify the system by name and standard number in the contract.