How do you calculate composite defect rate?

Divide the number of composite defects found by the number of parts or features inspected, then multiply by 100. With 11 defects across 240 parts inspected, that is 11 ÷ 240 × 100 = 4.58%.

What is a good composite defect rate?

It depends on the process and customer. Mature aerospace prepreg lines often run well under 2%, while early-stage infusion or hand-layup work can sit at 5-10%. In the worked example, 4.58% against a 3% target leaves a 1.58-point gap that needs closing.

Does the gap to target being negative mean I passed?

No — here the gap is calculated as rate minus target, so a positive number means you are over target. 4.58% minus a 3% target gives +1.58 points, meaning you exceeded the allowed defect rate by 1.58 points.

Should I count parts or features inspected?

Be consistent. If you inspect at the feature level (each ply boundary, each bond line), use feature count; if you accept or reject whole parts, use part count. Mixing the two inflates or deflates the rate and breaks trend comparisons.

Defect rate vs first-pass yield — what's the difference?

Defect rate counts total defects against units inspected, so one part can carry several defects. First-pass yield counts good units against total units, so it caps at one defect-event per part. Use yield for flow and capacity, defect rate for process-fault intensity.

Why is my composite defect rate spiking on one shift?

Common causes are vacuum bag leaks, expired or cold prepreg, inconsistent debulk, or a drifting autoclave ramp. Trend the rate by shift and cross it with the defect Pareto to isolate whether it is a material, tooling, or operator-technique issue.

Composites, Fiberglass & Advanced Materials calculator

Composite Defect Rate Calculator

Composite Defect Rate is the percentage of inspected composite parts or features that fail quality criteria — delamination, dry spots, porosity, fiber wash, voids, or resin-starved areas. Quality engineers and lamination supervisors in aerospace, wind, and marine composites track it shift-by-shift because composite rework is expensive and often impossible: a delaminated carbon laminate usually scraps, it doesn't re-cure. Watching the rate against a target tells you whether your layup, vacuum integrity, and cure cycle are in control before a batch of high-value parts is committed. It is the single most-watched first-pass quality number on most prepreg and infusion lines.

What this calculator does

Calculate defect rate for composite layup, cure, trim, inspection, or finishing operations.
tracking composite manufacturing defect rate
It divides composite defects found by composite parts or features inspected and multiplies by 100 to give a defect rate, then subtracts your target to show the gap in percentage points.

Formula used

Composite Defect Rate = composite defects found ÷ composite parts or features inspected × 100
Gap to target = Composite Defect Rate - target composite defect rate

Inputs explained

composite defects found: Count defects, nonconformances, inspection findings, NDI indications, cosmetic flaws, or MRB records.
composite parts or features inspected: Use parts, panels, plies, bondlines, coupons, or inspection features checked in the same scope.
target composite defect rate: Use the control-plan, customer, launch, or historical defect-rate target.

How to use the result

Use it at end-of-shift or per build batch to convert raw inspection counts into a rate you can trend and compare against an internal AQL or customer requirement.
A rate alone hides defect severity and Pareto — one critical delamination and one cosmetic resin run both count as a single defect, so pair it with a defect-type breakdown before acting.

Current U.S. benchmarks

The producer price index for plastic resins and materials stands at 319.371 (BLS, May 2026), up 19.5% from a year earlier. Quotes priced off last quarter's material cost miss this move.
Steel mill PPI stands at 348.53 (BLS, May 2026), up 6.7% from a year earlier. New factory orders are up 2.3% year over year (Census).

Common questions

How do you calculate composite defect rate? Divide the number of composite defects found by the number of parts or features inspected, then multiply by 100. With 11 defects across 240 parts inspected, that is 11 ÷ 240 × 100 = 4.58%.
What is a good composite defect rate? It depends on the process and customer. Mature aerospace prepreg lines often run well under 2%, while early-stage infusion or hand-layup work can sit at 5-10%. In the worked example, 4.58% against a 3% target leaves a 1.58-point gap that needs closing.
Does the gap to target being negative mean I passed? No — here the gap is calculated as rate minus target, so a positive number means you are over target. 4.58% minus a 3% target gives +1.58 points, meaning you exceeded the allowed defect rate by 1.58 points.
Should I count parts or features inspected? Be consistent. If you inspect at the feature level (each ply boundary, each bond line), use feature count; if you accept or reject whole parts, use part count. Mixing the two inflates or deflates the rate and breaks trend comparisons.
Defect rate vs first-pass yield — what's the difference? Defect rate counts total defects against units inspected, so one part can carry several defects. First-pass yield counts good units against total units, so it caps at one defect-event per part. Use yield for flow and capacity, defect rate for process-fault intensity.

Last reviewed 2026-05-12.