What regrind limit should I enter?

Use the lower of the customer print and the resin supplier's guidance, or 0 if regrind is banned. DuPont's nylon guide sets it per part by testing, preferably at most 25% blended with virgin.

Does a hot runner always cut resin cost per part?

Only when runner scrap exceeds what you can regrind. If the regrind limit already absorbs the runner, the resin saving is zero; the case rests on cycle time and part quality.

Why a reject rate instead of a waste factor?

You can read it off your scrap log, and rejects compete with the runner for the regrind allowance. A waste factor mixes rejects, purge and startup into one guess.

Should resin price include freight and color?

Yes: use the delivered price per kg, including freight and surcharges. If you add color concentrate at the press, blend its cost in at your let-down ratio.

Injection Molding calculator

Resin Cost per Part Calculator

Find the resin cost of each good part once runner, rejects and your regrind limit are counted: the material line of a quote. You need part and runner weights, cavities, reject rate, regrind limit and resin price.

What this calculator does

Resin cost of each good molded part, counting runner, rejects and the regrind your print allows.

Formula used

Shot weight = part weight × cavities + sprue and runner
Good parts per shot = cavities × (1 − reject rate)
Regrind used per shot = lesser of (shot weight − good parts per shot × part weight) and (regrind limit × shot weight)
Resin cost per good part = (shot weight − regrind used) ÷ good parts per shot × resin price ÷ 1,000 g per kg
Runner and reject loss = resin cost per good part − part weight × resin price ÷ 1,000

Inputs explained

Part Weight: Weigh a good part without its runner, or use CAD mass.
Sprue and Runner per Shot: Cold sprue and runner from one shot; 0 for a hot runner.
Cavities: Cavities running, excluding any blocked off.
Reject Rate: Rejected parts as a share of parts molded, from your scrap log.
Regrind Limit: Customer print or resin datasheet limit; 0 if regrind is banned.
Delivered Resin Price: Invoice price per kg including freight and surcharges.

How to use the result

Best suited to material line of a new part quote, savings from a hot runner or smaller runner, repricing after a resin price change.
Purge, startup and color-change losses are per run; count them in Scrap Resin Cost. Your regrind limit must come from part testing or the customer print; this page does not validate it.

Current U.S. benchmarks

The producer price index for plastic resins and materials stands at 280.569 (BLS, Aug 2026), up 6.6% 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

What regrind limit should I enter? Use the lower of the customer print and the resin supplier's guidance, or 0 if regrind is banned. DuPont's nylon guide sets it per part by testing, preferably at most 25% blended with virgin.
Does a hot runner always cut resin cost per part? Only when runner scrap exceeds what you can regrind. If the regrind limit already absorbs the runner, the resin saving is zero; the case rests on cycle time and part quality.
Why a reject rate instead of a waste factor? You can read it off your scrap log, and rejects compete with the runner for the regrind allowance. A waste factor mixes rejects, purge and startup into one guess.
Should resin price include freight and color? Yes: use the delivered price per kg, including freight and surcharges. If you add color concentrate at the press, blend its cost in at your let-down ratio.

Related guides

Last reviewed 2026-10-01.