Injection Molded Plastic Part Cost Calculator
Quoting molded parts means stacking resin, machine time, labor, scrap, packaging, secondary work and tool cost into one price per good part. This calculator does that stack so you can test what happens when cycle time, scrap or resin price moves.
Your numbers
Use 0 for hot runner.
Share of runner weight that returns to the process at no resin cost.
Depreciation, energy, floor space, maintenance.
Pad print, ultrasonic weld, assembly, inspection.
Your results
Planning estimate. Add margin, overhead, quality costs and logistics according to your own costing policy.
Total cost per part vs scrap rate
Sweeps Scrap rate from 0 to 20, holding your other inputs fixed.
Review how molded part costs flow into your ERP
Optional: a short review of routing, scrap and rate setup for molded parts.
Optional. The tool and every export work without this. No spam.
How to use it
Enter part and runner weight, resin price, cavity count and cycle time. Add the press hourly rate and labor rate, with operators per press as a fraction when one operator tends several machines. Enter scrap percent, packaging, secondary operation cost, mold cost and the number of parts you expect to amortize it over. The outputs show each cost element and the total cost per good part.
- Use a full machine hour rate, not just energy.
- Express shared operators as a fraction.
- Amortize the mold over expected program volume.
- Run the scrap sweep chart before quoting.
How the cost is built
Material cost per part is part weight plus the runner share per cavity that is not recovered, multiplied by resin price per kilogram. Machine and labor cost per part are hourly rates divided by parts per hour, where parts per hour equals 3600 times cavities divided by cycle time. Material, machine and labor are divided by one minus scrap rate to put the cost of rejected parts on the good ones. Packaging, secondary work and mold amortization are then added after scrap, since those costs normally apply only to good parts.
Reading the result
With the defaults, the total comes to about eleven cents a part, with material the largest piece. Notice that cycle time acts on machine and labor cost directly, while resin price acts on the material line, so the right lever depends on the part. The scrap chart shows how a two or three point move changes price on high-volume parts. If tooling is more than 20 percent of the total, the quote depends heavily on the volume assumption and you should state it in the offer.
Common mistakes
Quoting with an optimistic cycle time from a lab trial instead of a proven production cycle is the most expensive error. Others include ignoring runner losses on cold runner tools, forgetting resin drying, color masterbatch and purge, treating regrind as free without counting grinding and handling, and leaving out mold maintenance. Setup and changeover time should be added if run lengths are short.
Frequently Asked Questions
How do you calculate the cost of an injection molded part?
Add material (part plus unrecovered runner at resin price), machine time and labor per part (hourly rates divided by parts per hour), then apply scrap, and add packaging, secondary operations and mold amortization.
What is a typical machine hour rate?
It varies widely by press size, region and how overhead is allocated. Small presses may be tens of dollars per hour and large presses well above a hundred. Use your own costed rate, not a market guess.
How should I amortize tooling?
Divide mold cost by the expected parts over the program, or charge it separately as a one-time tooling fee. The first option makes the price depend on volume, so state the volume.
Does regrind reduce part cost?
It reduces virgin resin purchases for the share you reuse, but costs grinding, handling and possible property loss. This tool treats a chosen share of runner weight as recovered at no resin cost.
If your ERP standard costs for molded parts rarely match what the plant sees, we can help review how routings, scrap and machine rates are set up.
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