Material Cost Per Part Calculator
Calculate total cost per injection-molded part including material (with runner waste and regrind), machine time, and overhead. Shows cost breakdown percentages.
About this calculator
The true cost of an injection-molded part is rarely just "part weight times resin price" — this calculator builds the full stack. On the material side, it adds the runner and sprue weight (waste that's created every shot but isn't part of the finished piece) to the part weight, then subtracts back out whatever fraction of that runner can be reground and reused, and finally inflates the result by the scrap rate so the good parts absorb the cost of the ones that get rejected. That net material figure, priced against resin cost per kilogram, becomes the material cost per part.
On the machine side, cost per part comes from cycle time and cavitation: parts per hour = (3600 / cycleTimeSec) × numCavities, and the machine's hourly rate is spread across that hourly output — so doubling the cavity count or shaving seconds off the cycle both directly cut machine cost per part, while overhead (labor, facility, quality) is spread the same way. Summing material, machine, and overhead gives the total cost per part, along with the percentage each component contributes so you can see whether a project is material-dominated (commodity resin, thin walls) or cycle-dominated (thick sections, long cooling, few cavities). One thing worth double-checking before trusting a quote built on this: it assumes a 100%-uptime run rate with no allowance for changeovers, mold maintenance, or line stoppages, and it doesn't include tooling amortization — those all sit on top of the per-part number this tool produces.
Inputs
Results
Total cost per part ($)
$0.73
How to Use This Calculator
- Enter Part weight (g), Resin price ($/kg), and Cycle time (sec).
- Set Number of cavities, Machine rate ($/hr), and Runner waste (%).
- Adjust Regrind recovery (%), Scrap rate (%) as needed.
- Review the Total cost per part ($) ($) result.
- Use Material cost per part ($) ($) and Machine cost per part ($) ($) to inform your decision.
How the result changes with Cycle time (sec)
| Cycle time (sec) | Total cost per part ($) |
|---|---|
| 15 | $0.40 |
| 23 | $0.58 |
| 45 | $1.06 |
| 75 | $1.73 |
What each input means
- Part weight (g)
- Net weight of the finished part in grams.
- Resin price ($/kg)
- Material cost per kilogram of virgin resin.
- Cycle time (sec)
- Total injection molding cycle time in seconds.
- Number of cavities
- Number of cavities in the mold.
- Machine rate ($/hr)
- Fully burdened machine hourly rate.
- Runner waste (%)
- Runner/sprue weight as % of part weight. 0% for hot runner.
- Regrind recovery (%)
- Percentage of runner waste that can be regrind and reused.
- Scrap rate (%)
- Percentage of parts rejected as scrap.
- Overhead rate ($/hr)
- Labor, facility, and quality overhead per hour.
What each result means
- Total cost per part ($)
- Sum of material, machine, and overhead costs per good part.
- Material cost per part ($)
- Material cost including waste and scrap allowance.
- Machine cost per part ($)
- Machine time cost per part.
- Overhead cost per part ($)
- Labor and facility overhead per part.
- Material %
- Material cost as percentage of total.
- Machine %
- Machine cost as percentage of total.
- Overhead %
- Overhead as percentage of total.
- Parts per hour
- Production rate considering cavities and cycle time.
- Cost per 1,000 parts ($)
- Total cost for a batch of 1,000 good parts.
- Effective material per part (g)
- Actual material consumed per good part including waste.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersPart weight (g) = 25, Resin price ($/kg) = 2.5, Cycle time (sec) = 30, Number of cavities = 1 = 9 input(s) provided
- Calculate Total cost per partTotal cost per part = materialCostPerPart + machineCostPerPart + overheadCostPerPart0.7315 = $0.732
- Calculate Material cost per partMaterial cost per part = (effectiveMaterialG / 1000) * resinPricePerKg0.0648 = $0.065
- Calculate Machine cost per part0.5 = $0.5
Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why does adding cavities to the mold cut machine cost per part but leave material cost per part unchanged?
Parts per hour is (3600 / cycleTimeSec) × numCavities, and both machine cost and overhead cost per part are the hourly rate divided by that parts-per-hour figure — so more cavities spread the same hourly rate over more parts. Material cost per part, by contrast, is computed purely from part weight, runner waste, regrind, and scrap rate, none of which depend on how many cavities the mold has.
How does the regrind recovery percentage lower my material cost?
The net material per part is partWeight + runnerWeight − (runnerWeight × regrindPct / 100), so a higher regrind recovery percentage subtracts more of the runner weight back out before the scrap-rate inflation is applied. At 100% regrind recovery the runner effectively costs nothing extra; at 0% the full runner weight is charged as if it were part material.
Why is the scrap rate applied as a division instead of just adding a percentage on top?
Effective material per part is netMaterial ÷ (1 − scrapRatePct / 100), which inflates the required material so the good parts collectively absorb the material cost of the rejected ones. This is the standard way to spread reject cost: at a 2% scrap rate you divide by 0.98, meaning the good parts carry a little over 2% extra material cost, not exactly 2%.
What do the material/machine/overhead percentage breakdowns actually tell me?
They show which cost driver dominates the part's economics. A project with a high material percentage is typically running commodity resin in thin-walled parts, where resin cost swamps machine time, while a high machine percentage points to a cycle-dominated part — thick sections, long cooling, or too few cavities — where speeding up the cycle or adding cavities would move the needle more than a cheaper resin would.
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