How do you calculate plastic injection-molding cost per part?

Multiply lot size by resin and cycle cost per part, apply the QC pass rate, add mold setup, then divide by lot size. For 5,000 parts at $0.85, 97% pass, and $180 setup, total is $4,302.50 and per part is about $0.86.

What does the QC pass rate do in this calculation?

It weights the variable cost to reflect that defective parts still consumed resin and cycle time. At 97% pass on a 5,000-part lot, variable cost is $4,122.50 rather than the full $4,250 at 100%.

What is a good dimensional QC pass rate for molded office products?

Mature high-cavitation tools for office and school plastics typically run 97-99%+ first-pass yield. Below about 95%, scrap and rework start eroding margin fast on low-price institutional parts.

Why include mold setup and first-article separately?

Mold setup is a one-time fixed cost independent of volume. Spreading $180 over 5,000 parts adds only $0.036 per part, but over a 500-part sample run it would add $0.36, so isolating it shows volume sensitivity clearly.

How does resin and cycle cost per part break down?

It bundles the resin weight times material price plus the machine rate times cycle time per part. For office plastics, a faster cycle or lighter wall section directly lowers this number, which is why it dominates the $4,122.50 variable cost in the example.

How can I drive cost per good part down on a molding run?

Improve first-pass yield, shorten cycle time, or run a larger lot to dilute the $180 setup. The biggest lever here is usually cycle time, since resin and cycle cost makes up over 95% of the $4,302.50 total.

Office, School & Institutional Products calculator

Plastic component cost Calculator

Plastic component cost calculates the loaded cost of an injection-molded run of office and school plastics, such as binder spines, pencil cases, locker hooks, and chair shells. Process engineers and cost estimators use it to translate resin price, cycle time, scrap, and one-time mold setup into a defensible cost per good part. Because these institutional SKUs ship in high volumes at low unit prices, even a one-point shift in dimensional QC pass rate or a few cents of resin and cycle cost moves the whole quote. Running this before tooling is committed keeps a high-cavitation program from going underwater.

What this calculator does

Estimates plastic component cost from the molded part count, resin and cycle cost per part, the share passing dimensional QC, and a flat mold-setup charge.
A molding cost estimator uses it to price the injection-molded trim, brackets, and fittings going into office and institutional furniture or fixtures.
It computes total molded-lot cost as lot size times per-part cost weighted by the QC pass rate, plus mold setup, then divides by lot size for cost per good part.

Formula used

Total plastic component cost = parts in lot x cost per part x QC pass rate + mold setup
Cost per good part = total / parts in lot

Inputs explained

Molded parts in the production lot:
Resin & cycle cost per part:
Parts passing dimensional QC:
Mold setup & first-article:

How to use the result

Use it when quoting or reviewing an injection-molding run and you need the effect of scrap and one-time tooling baked into a per-part number.
The QC pass rate scales the variable cost but the divisor uses total lot size, so the per-unit figure reflects cost spread over the full lot rather than over good parts only.

Common questions

How do you calculate plastic injection-molding cost per part? Multiply lot size by resin and cycle cost per part, apply the QC pass rate, add mold setup, then divide by lot size. For 5,000 parts at $0.85, 97% pass, and $180 setup, total is $4,302.50 and per part is about $0.86.
What does the QC pass rate do in this calculation? It weights the variable cost to reflect that defective parts still consumed resin and cycle time. At 97% pass on a 5,000-part lot, variable cost is $4,122.50 rather than the full $4,250 at 100%.
What is a good dimensional QC pass rate for molded office products? Mature high-cavitation tools for office and school plastics typically run 97-99%+ first-pass yield. Below about 95%, scrap and rework start eroding margin fast on low-price institutional parts.
Why include mold setup and first-article separately? Mold setup is a one-time fixed cost independent of volume. Spreading $180 over 5,000 parts adds only $0.036 per part, but over a 500-part sample run it would add $0.36, so isolating it shows volume sensitivity clearly.
How does resin and cycle cost per part break down? It bundles the resin weight times material price plus the machine rate times cycle time per part. For office plastics, a faster cycle or lighter wall section directly lowers this number, which is why it dominates the $4,122.50 variable cost in the example.

Last reviewed 2026-05-12.