Injection Molding Resin Price Increase Impact Calculator
A resin price letter lands and the first question from sales is how much to ask for per part. This calculator turns the new price per pound into cost per part, margin and annual dollars, using the real runner, scrap and regrind picture instead of the drawing weight alone.
Your numbers
Net weight of one molded part, from the part drawing or a weighed sample.
Total cold runner plus sprue weight per shot. Enter 0 for a hot runner mold.
Percent of parts molded that are rejected (start-up, defects).
Share of runner and scrap that is ground and run back in, displacing virgin resin.
Delivered price per pound from your PO or last invoice.
Machine time, labor, packaging, tooling amortization and overhead per part.
Your results
Planning estimate. Assumes regrind displaces virgin resin one for one at the same price and that no regrind is sold or discarded. Add drying, color concentrate and additive cost to the resin price if they are bought per pound.
Annual profit impact vs new resin price
Sweeps New resin price from 0.6 to 2.2, holding your other inputs fixed.
Resin cost exposure report from your ERP
Optional: we can sketch how to pull resin usage and part margin from your ERP so you see exposure per customer before the next price letter.
Optional. The tool and every export work without this. No spam.
How to use it
Enter the net part weight, cavity count and total runner weight per shot (zero for hot runner). Add your scrap rate and the share of runner and scrap you actually regrind and reuse. Then enter the current and new delivered price per pound and your cost and price per part. The primary results are the per-part cost increase and the annual dollar impact. The chart sweeps the new resin price so you can show a customer or a buyer what the exposure looks like at several quotes.
The math behind the numbers
Resin processed per good part is shot weight divided by cavities, divided by one minus the scrap rate. Anything above the net part weight is runner and scrap. A share of that comes back as regrind and offsets virgin purchases. Net virgin grams divided by 453.592 gives pounds per part, which is multiplied by price per pound. Margin is price minus resin minus all other cost, divided by price. To hold margin percent the price becomes cost divided by one minus the original margin percent.
- Pounds per part = net virgin grams / 453.592
- Annual impact = (new cost - old cost) x annual volume
- Hold-margin price = (new resin + other cost) / (1 - old margin %)
Reading the result
With the defaults, a 25 percent resin increase is only about 2.4 cents on a 42 cent part, yet it moves margin by several points and costs over $14,000 a year at 600,000 parts. Notice two things. A hot runner mold and a low scrap rate shrink the exposure because less resin is processed per good part. And holding margin percent requires slightly more than holding margin dollars, because the cost increase is itself marked up. Decide which rule your customer contract allows before you quote.
Common mistakes
Using the drawing weight and ignoring the runner is the most common error on cold runner tools, and it understates cost by 5 to 25 percent. Others are assuming 100 percent regrind reuse when the customer limits it, mixing up price per pound and per kilogram, and forgetting that color masterbatch and additives are bought per pound too.
- Check customer limits on regrind percentage (many medical and food parts allow none)
- Use delivered price, not the ex-works quote
- Update the price in your ERP item cost after the contract changes
Frequently Asked Questions
Why does a 25 percent resin increase not mean a 25 percent part cost increase?
Resin is only one cost element of a molded part, along with machine time, labor, packaging and tooling. If resin is about a quarter of the total part cost, a 25 percent resin increase raises total cost by roughly 6 percent. The calculator shows both numbers.
How is regrind handled?
Runner and scrap grams are assumed to be ground and reused in place of virgin resin at the percentage you enter. If your customer prohibits regrind or you sell it at a discount, set the slider to zero and adjust the other cost line for the sale value.
Should I pass through the increase per pound or per part?
Per part is simplest to administer and is what the calculator computes. A per-pound adjustment tied to a published index is fairer for long contracts, and the clause template in this tool set shows how to write it.
What resin price should I enter?
Use the delivered price per pound you actually pay, including freight, color concentrate and any additive. List prices or index values rarely equal your invoice price, and the difference changes the result.
If resin costs live in your ERP item master and PO history, Netray can build a read-only agent that flags every molded part whose margin drops below target when a resin index moves.
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Guides
- Handling Resin Price Increases in Injection Molding QuotesHow injection molders handle resin price swings in quotes: index clauses, quote validity, material surcharges, pass-through rules and ERP price tracking.
- Tracking Scrap, Runners and Regrind in Your Injection Molding ERPHow injection molders track scrap, runners and regrind in the ERP: reason codes, material reconciliation, regrind blend limits and costing the recovered resin.
- Injection Molding Job Costing: Finding Where Quoted Margin DisappearsHow injection molders find margin leaks: compare quoted and actual cycle, scrap, resin and downtime by job and part, and fix machine rates and overhead.
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