How do you calculate resin cost per part?

Divide the part's shot weight in grams by 1000 to get kilograms, multiply by the resin price per kg, then multiply by your waste factor. For a 32 g part at $2.85/kg with a 1.05 waste factor, the base material is $0.0912 and the waste-adjusted cost rises from there.

Should runner weight be included in shot weight?

Yes, unless the runner is fully reground and reused at no loss. On a cold-runner tool, allocate each cavity's share of the runner into the part weight, since you pay for that resin even if some is recovered as regrind.

What is a typical waste or overage factor?

Most shops use 1.03 to 1.08 (3% to 8%) to cover startup shots, purging, and color changes. Tight-tolerance or high-scrap parts may justify more; well-controlled high-volume jobs trend toward the low end.

Why convert grams to kilograms in the formula?

Resin is priced per kilogram but parts are weighed in grams, so you divide grams by 1000 before multiplying by $/kg. Skipping this step overstates cost by a factor of 1,000.

How much does resin price affect part cost?

Directly and linearly. A 10% resin price increase raises resin cost per part by 10%. Because resin is often the biggest variable cost, indexing your quote to a published resin price protects margin when the market moves.

Resin cost per part vs fully loaded part cost — what is the difference?

Resin cost per part is material only. Fully loaded cost adds machine hourly rate divided by parts per hour, direct labor, colorant and additives, packaging, scrap beyond the waste factor, and amortized tooling. Resin is usually the largest single piece but rarely the whole picture.

Injection Molding calculator

Resin Cost Per Part Calculator

Resin cost per part is the raw-material dollar amount in a single molded part, built from the part's shot weight (including its share of the runner), the resin price per kilogram, and a waste factor for startup scrap and overage. Estimators and cost engineers rely on it because resin is typically the largest variable cost in a molded part, and a few cents of error multiplied across a million parts swings a program's margin. It is the foundation of any molding quote and the first number to revisit when resin prices move. Buyers also use it to benchmark supplier pricing against part weight.

What this calculator does

Calculate material cost per molded part from part weight, runner scrap allocation, and resin price per kilogram.
Use this when building part cost breakdowns, comparing resin grades, or estimating material savings from weight reduction or hot runner conversion.
It computes the per-part resin dollar cost by converting shot weight to kilograms, multiplying by resin price, and applying a waste factor.

Formula used

Resin cost per part = (Material per part / 1000) x Resin price x Waste factor
Divide weight by 1000 to convert grams to kilograms before multiplying by $/kg

Inputs explained

Shot weight per part including runner share:
Resin purchase price:
Scrap/overage allowance factor:

How to use the result

Use it when quoting a part, re-pricing after a resin index change, or evaluating whether a lighter-weight redesign pays for itself.
It captures only resin cost — not machine rate, labor, colorant, additives, or amortized tooling — so it is a material cost, not a fully loaded part cost.

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.
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 resin cost per part? Divide the part's shot weight in grams by 1000 to get kilograms, multiply by the resin price per kg, then multiply by your waste factor. For a 32 g part at $2.85/kg with a 1.05 waste factor, the base material is $0.0912 and the waste-adjusted cost rises from there.
Should runner weight be included in shot weight? Yes, unless the runner is fully reground and reused at no loss. On a cold-runner tool, allocate each cavity's share of the runner into the part weight, since you pay for that resin even if some is recovered as regrind.
What is a typical waste or overage factor? Most shops use 1.03 to 1.08 (3% to 8%) to cover startup shots, purging, and color changes. Tight-tolerance or high-scrap parts may justify more; well-controlled high-volume jobs trend toward the low end.
Why convert grams to kilograms in the formula? Resin is priced per kilogram but parts are weighed in grams, so you divide grams by 1000 before multiplying by $/kg. Skipping this step overstates cost by a factor of 1,000.
How much does resin price affect part cost? Directly and linearly. A 10% resin price increase raises resin cost per part by 10%. Because resin is often the biggest variable cost, indexing your quote to a published resin price protects margin when the market moves.

Last reviewed 2026-05-12.