How do you calculate regrind percentage?

Divide the regrind weight per shot by the total shot weight, then multiply by 100. With 12 g of regrind in a 56 g shot, that is 12 / 56 x 100 = 21.4% regrind.

What is the maximum regrind percentage allowed?

It depends on the resin and the part spec, but suppliers commonly cap virgin-grade blends at 20% to 30% regrind. Critical structural or appearance parts may require 0% (virgin only), while non-critical parts can run higher.

Is 21% regrind too much?

In the worked example, 21.4% sits at the low end of the typical 20-30% allowance, so it is usually acceptable — but always confirm against your specific resin datasheet and customer print, which override any general rule.

Does high regrind percentage hurt part quality?

It can. Each regrind pass shortens polymer chains, reducing impact strength and altering color and flow. The percentage in the shot plus the number of prior regrind passes together determine how much properties degrade.

What is the difference between regrind percentage and regrind passes?

Percentage is how much regrind is in one shot; passes is how many heat histories that material has accumulated. You can hit a 20% target with first-pass regrind safely, but 20% of fifth-pass material may already be out of spec.

How do I lower my regrind percentage?

Reduce the granulator's contribution to the hopper blend, improve first-pass yield so you generate less scrap, or add more virgin resin. Reducing runner weight with a hot-runner tool also cuts the regrind you produce.

Injection Molding calculator

Regrind Percentage Calculator

Regrind percentage is the share of recycled, reground material in each injection molding shot, calculated as regrind weight divided by total shot weight. Process engineers and quality teams watch it because every resin supplier and customer spec sets a maximum regrind level — commonly 20% to 30% — above which mechanical properties, color, and appearance can degrade. Running too much regrind saves money but risks field failures and spec violations; running too little wastes recoverable material. This calculator keeps your blend inside the allowed window. It is the everyday check before a granulator's output goes back into the hopper.

What this calculator does

Calculate the regrind content as a percentage of total shot weight to stay within resin supplier and quality limits.
Use this to verify that your regrind blend ratio stays within the resin supplier maximum (typically 15% to 30%) and your internal quality specification.
It computes the percentage of a shot made up of regrind by dividing regrind weight by total shot weight and multiplying by 100.

Formula used

Regrind percentage = (Regrind weight / Total shot weight) x 100
Compare to resin supplier max (typically 20% to 30%) and your quality spec

Inputs explained

Regrind weight blended per shot:
Total shot weight (virgin plus regrind):

How to use the result

Use it when setting or auditing a regrind blend ratio, validating against a customer or resin-supplier maximum, or troubleshooting property drift in molded parts.
It only measures the weight ratio in a single shot; it does not track how many times the material has been reground, which compounds property loss independent of the percentage.

Current U.S. benchmarks

The producer price index for plastic resins and materials stands at 319.371 (BLS, May 2026), up 19.5% 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

How do you calculate regrind percentage? Divide the regrind weight per shot by the total shot weight, then multiply by 100. With 12 g of regrind in a 56 g shot, that is 12 / 56 x 100 = 21.4% regrind.
What is the maximum regrind percentage allowed? It depends on the resin and the part spec, but suppliers commonly cap virgin-grade blends at 20% to 30% regrind. Critical structural or appearance parts may require 0% (virgin only), while non-critical parts can run higher.
Is 21% regrind too much? In the worked example, 21.4% sits at the low end of the typical 20-30% allowance, so it is usually acceptable — but always confirm against your specific resin datasheet and customer print, which override any general rule.
Does high regrind percentage hurt part quality? It can. Each regrind pass shortens polymer chains, reducing impact strength and altering color and flow. The percentage in the shot plus the number of prior regrind passes together determine how much properties degrade.
What is the difference between regrind percentage and regrind passes? Percentage is how much regrind is in one shot; passes is how many heat histories that material has accumulated. You can hit a 20% target with first-pass regrind safely, but 20% of fifth-pass material may already be out of spec.

Last reviewed 2026-05-12.