How do you calculate defect rate by cavity?

Divide the rejected parts from that cavity by the total parts produced from the same cavity, then multiply by 100. With 12 rejects out of 500 parts the cavity defect rate is 2.4%.

What is a good defect rate for an injection mold cavity?

It depends on the part, but most production molds target under 1–2% per cavity. The 2.4% in the example is above a 0% target, meaning this cavity is a candidate for maintenance compared to its siblings.

Why measure defect rate per cavity instead of per mold?

A mold average hides outliers. If the tool averages 1% but one cavity runs 2.4%, that single cavity is producing far more than its share of scrap and is the one worth fixing.

How many parts do I need before the cavity rate is meaningful?

With small runs one bad part dominates the percentage. At 500 parts (the example) each reject moves the rate 0.2 points, which is stable enough to compare cavities; under ~100 parts treat the number cautiously.

What does a high defect rate on one cavity usually indicate?

Localized issues: a worn or unbalanced gate, a clogged vent, cooling-line imbalance, or core damage in that specific cavity. The calculator points you there; cavity inspection confirms it.

How do I use this to schedule mold maintenance?

Rank all cavities by defect rate and target the worst offenders first. A cavity sitting at 2.4% against a fleet average near 1% jumps the queue for cleaning, polishing, or repair.

Injection Molding calculator

Defect Rate by Cavity Calculator

Defect Rate by Cavity is the percentage of parts from one specific mold cavity that are rejected, isolated from the rest of the tool. Process engineers and mold maintenance teams use it because a multi-cavity mold can run at an acceptable average while one worn or fouled cavity quietly produces most of the scrap. Tracking each cavity separately turns a vague 'the mold is making bad parts' into a targeted action — vent that cavity, polish that core, or block it off — and protects yield without pulling the whole tool.

What this calculator does

Calculate the defect rate for a specific mold cavity to identify problem cavities that need maintenance or correction.
Use this to compare reject rates across cavities, identify cavities needing maintenance, or track quality improvement after mold repairs or process adjustments.
It computes the reject percentage for a single cavity by dividing that cavity's rejected parts by the total parts it produced.

Formula used

Cavity defect rate = (Rejected parts / Total parts from cavity) x 100
Compare across cavities to identify outliers needing mold maintenance

Inputs explained

Rejected parts from this cavity:
Total parts produced from this cavity:

How to use the result

Use it when sorting scrap by cavity number on a multi-cavity mold, during a yield investigation, or to prioritize which cavities get attention at the next PM.
It only flags which cavity is bad, not why — you still need to inspect the cavity for the root cause (gate wear, venting, cooling imbalance), and small sample sizes make a single reject swing the rate.

Current U.S. benchmarks

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The U.S. has 9,635 plastics product manufacturing establishments employing about 677,302 workers (Census County Business Patterns, 2023).

Common questions

How do you calculate defect rate by cavity? Divide the rejected parts from that cavity by the total parts produced from the same cavity, then multiply by 100. With 12 rejects out of 500 parts the cavity defect rate is 2.4%.
What is a good defect rate for an injection mold cavity? It depends on the part, but most production molds target under 1–2% per cavity. The 2.4% in the example is above a 0% target, meaning this cavity is a candidate for maintenance compared to its siblings.
Why measure defect rate per cavity instead of per mold? A mold average hides outliers. If the tool averages 1% but one cavity runs 2.4%, that single cavity is producing far more than its share of scrap and is the one worth fixing.
How many parts do I need before the cavity rate is meaningful? With small runs one bad part dominates the percentage. At 500 parts (the example) each reject moves the rate 0.2 points, which is stable enough to compare cavities; under ~100 parts treat the number cautiously.
What does a high defect rate on one cavity usually indicate? Localized issues: a worn or unbalanced gate, a clogged vent, cooling-line imbalance, or core damage in that specific cavity. The calculator points you there; cavity inspection confirms it.

Last reviewed 2026-05-12.