How do you calculate a resin mix ratio?

Divide the resin base amount by the hardener amount, then apply your reporting conversion. With 100 parts resin to 28 parts hardener and a conversion of 1, the ratio is about 3.57:1, meaning 3.57 parts resin per part of hardener.

What does a 100:28 epoxy ratio mean?

It means 100 parts of resin to 28 parts of hardener by the data-sheet basis. Expressed as a single number that is 3.5714:1, so for every part of hardener you add roughly 3.57 parts of resin.

Is resin mix ratio by weight or by volume?

It can be either, and the two are not interchangeable because resin and hardener have different densities. Always use the basis your data sheet specifies; this calculator computes the ratio but does not convert weight to volume.

What happens if I get the mix ratio wrong?

Off-ratio thermosets undercure or overcure: too little hardener leaves a soft, tacky, low-Tg part, and too much can make it brittle and exothermic. Even small errors degrade strength and chemical resistance, so weigh, do not eyeball.

How do I scale a mix ratio to my batch size?

Keep the ratio fixed and multiply both components by the same factor. The 3.5714:1 result holds whether you mix 128 grams or 12.8 kg; only the absolute amounts change.

Why is the conversion factor set to 1?

A conversion of 1 reports the ratio in its natural form, 3.5714:1. You would change it only to rescale into an alternate reporting convention, such as expressing the proportion against a base of 100.

Composites, Fiberglass & Advanced Materials calculator

Resin Mix Ratio Calculator

Resin Mix Ratio is the proportion of base resin to hardener, catalyst, or additive that drives a thermoset to a full, properly crosslinked cure. Laminators, potting and casting techs, and adhesive bonders rely on it because an off-ratio mix never reaches design Tg, stays tacky, or cures brittle. Epoxies in particular are unforgiving: the ratio is set by reaction stoichiometry, not by eye. This calculator returns the ratio in a clean by-weight or by-volume form and lets you rescale it to whatever reporting convention your data sheet uses.

What this calculator does

Calculate resin-to-hardener or resin-to-catalyst mix ratio for composite resin systems.
checking resin, hardener, catalyst, or promoter proportion
It divides the resin base amount by the hardener or catalyst amount and applies a reporting conversion, giving the mix ratio as parts of resin per part of hardener.

Formula used

Resin Mix Ratio = resin base weight or volume ÷ hardener, catalyst, or additive amount
Converted resin mix ratio = resin mix ratio × mix-ratio reporting conversion

Inputs explained

Resin base amount:
Hardener, catalyst, or additive amount:
Mix-ratio reporting conversion:

How to use the result

Use it when setting up a batch, converting a data-sheet ratio to your scale, or checking that a measured weigh-out matches the manufacturer's specified proportion.
It is a proportion only; it does not validate that the data-sheet ratio is by weight versus by volume, and using the wrong basis will produce a correctly computed but wrong mix.

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.
Steel mill PPI stands at 348.53 (BLS, May 2026), up 6.7% from a year earlier. New factory orders are up 2.3% year over year (Census).

Common questions

How do you calculate a resin mix ratio? Divide the resin base amount by the hardener amount, then apply your reporting conversion. With 100 parts resin to 28 parts hardener and a conversion of 1, the ratio is about 3.57:1, meaning 3.57 parts resin per part of hardener.
What does a 100:28 epoxy ratio mean? It means 100 parts of resin to 28 parts of hardener by the data-sheet basis. Expressed as a single number that is 3.5714:1, so for every part of hardener you add roughly 3.57 parts of resin.
Is resin mix ratio by weight or by volume? It can be either, and the two are not interchangeable because resin and hardener have different densities. Always use the basis your data sheet specifies; this calculator computes the ratio but does not convert weight to volume.
What happens if I get the mix ratio wrong? Off-ratio thermosets undercure or overcure: too little hardener leaves a soft, tacky, low-Tg part, and too much can make it brittle and exothermic. Even small errors degrade strength and chemical resistance, so weigh, do not eyeball.
How do I scale a mix ratio to my batch size? Keep the ratio fixed and multiply both components by the same factor. The 3.5714:1 result holds whether you mix 128 grams or 12.8 kg; only the absolute amounts change.

Last reviewed 2026-05-12.