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Injection Molding Yield Loss Estimator

This Injection Molding Yield Loss Estimator estimates rejected molded parts, accepted parts, and yield from total produced quantity and reject rate. It gives quality and production teams a direct way to translate a defect percentage into physical units lost during a run.

Because multi-cavity molding can generate large quantities quickly, a small reject-rate change can represent a meaningful difference in good output. Use the estimator to review a completed batch or test a proposed quality improvement, while keeping in mind that it treats all rejects equally and does not assign different costs to resin, inserts, labor, or rework.

Molding yield inputs

parts
%
Result
—
estimated rejected molded parts
Estimated good parts—
Yield—
Good parts gained per 1-point reject reduction—

1. Enter total molded output
Use all parts produced in the selected run or period before separating good and rejected pieces.

2. Enter the reject percentage
Use the share of total output that does not qualify as good product under your reporting definition.

3. Read rejected quantity
The calculator converts the percentage loss into an estimated number of rejected parts.

4. Review good-part yield
Check remaining good output and the complementary yield percentage.

5. Evaluate quality gains
The one-percentage-point recovery figure shows how many additional good parts would result from reducing the reject rate by one point at the same total output.

Rejected parts = Total molded parts × Reject rate
Good parts = Total molded parts − Rejected parts
Yield = 100% − Reject rate

What the result means

The main result is the estimated number of molded parts classified as rejects at the entered reject rate.

This estimator does not distinguish scrap from rework or startup waste. Use the same classification rules that support your plant quality reporting.

Given: 18,500 molded parts with a 1.8% reject rate.

Calculation: Rejected parts = 18,500 × 0.018 = 333. Good parts = 18,500 − 333 = 18,167. Yield = 98.2%.

Result: 333 rejected parts and 18,167 good parts.

A one-percentage-point reduction in reject rate at the same volume would recover about 185 additional good parts.

Should short shots and flash both count in the reject rate?

Count any defect categories that your organization classifies as rejected output. Consistent inclusion rules matter more than the specific defect names.

How do I handle parts that are regrindable?

Physical parts can still be rejects even if material is later recovered. This calculator measures output loss, not net material cost.

Can the result be fractional?

Yes, because a percentage applied to a planning quantity may produce a fractional estimate. Actual discrete part counts are whole numbers.

Does cavity imbalance require a different formula?

Not for a simple total reject rate. If defects are concentrated by cavity, cavity-level analysis is more useful for diagnosis.

How can this support capacity planning?

Apply expected yield to gross throughput to estimate good output, especially when demand is stated in acceptable parts rather than total molded pieces.