Injection Molding Piece-Price Calculator

Step-by-step

2) Convert machine time to output

Good parts/hr = 3600 / Cycle time × Cavities × (1 – Scrap%)

This single line turns time into throughput and drives your processing $/part.

Good parts/hr = 249.43

3) Put real numbers on resin usage

Resin is consumed on every shot; regrind only offsets some runner cost later. A transparent way to handle this:

Material g/good part = (Part g + (1-Regrind%) × Runner g/cavity) / (1-Scrap%)
Material $/part = Material g/good part / 1000 × $/kg

Material g/good part = 25.26 g
Material $/part = $0.067

4) Turn hourly cost into processing cost per part

Loaded $/hr = Press + Labor + Overhead; Processing $/part = Loaded $/hr / Good parts/hr

Loaded $/hr = $70.00
Processing $/part = $0.281

5) Allocate setup and tooling fairly

Setup $/part = Setup hr × Loaded $/hr / Order qty    Tooling $/part = Tooling $ / Lifetime qty

Keep setup separate from tooling – setup scales by order size, tooling by lifetime.

Setup $/part = $0.007
Tooling $/part = $0.160

6) Add other per-part costs

Include packaging, labeling, QC/inspection (per lot or per unit – use per unit here for simplicity).

Other $/part = $0.030

7) Apply your margin to get price

Unit cost before margin = Material + Processing + Setup + Tooling + Other
Price = Unit cost before margin / (1 – Target margin)

Unit cost before margin = $0.545

Worked example (current inputs)

Inputs

Outputs

Cycles per hour: 128.57
Good parts per hour: 249.43
Total shot mass per cycle: 54.00 g (all cavities)
Effective material per good part: 25.26 g
Material $/part: $0.067
Hourly loaded rate: $70.00/hr
Processing $/part: $0.281
Setup $/part: $0.007
Tooling $/part: $0.160
Other $/part: $0.030
Unit cost before margin: $0.545
Selling price (25.0% margin): $0.727

Sanity check: Material lower bound = (Part g / 1000) × $/kg = 22/1000 × 2.65 = $0.058/part. If your quote is below this and you have cold runners, revisit your assumptions.

What-ifs you can show customers in one line

Hot runner vs. cold runner (this example): Setting runner g/cavity to 0 (hot runner) lowers material cost by ~$0.007/part at 50% regrind utilization and the same scrap rate – useful, but second-order vs. cycle/cavitation.
Cavitation (2 to 4 cavities): Processing $/part roughly halves (here: $0.281 to $0.140), but tool cost rises. Quote both to make ROI clear.
Cycle time ±10%: Unit cost shifts about ±5.2% in this setup.
Press rate +$10/hr: Unit cost +7.5%.
Scrap 3% to 5%: Unit cost +1.3% (material and throughput both take a hit).

Common pitfalls this model avoids

Burying runner cost: Explicitly separates runner mass and regrind credit.
Under-counting setup: Allocates setup to the order (not the lifetime), which protects you on small runs.
Mixing markup and margin: Uses margin consistently. If you prefer markup, swap the final step to Price = Cost × (1 + Markup).

Suggested visuals (drop these into the post)

Waterfall chart of cost components: Material to Processing to Setup to Tooling to Other to Price.
One-slider chart showing cycle time on the x-axis vs. piece cost.
Two-quote ROI callout: “2-cavity vs 4-cavity” comparing unit cost and simple payback for the higher-cavitation tool.

CTA ideas

Get a fast quote: “Send us your part weight and cycle time – we’ll return a transparent breakdown like the one above.”
DFM review: “Not sure on runner size or cycle time? Book a DFM review and we’ll estimate both.”
Hot runner ROI: “Considering a hot runner? We’ll run your numbers (scrap, color change, maintenance) and email a one-page ROI.”