What does 100 to 28 by weight mean?

For every 100 units of resin weight, add 28 units of hardener weight. Scale both by the same factor, so a 20 lb batch takes 5.6 lb of hardener.

Can I mix by volume instead of by weight?

Only with a chart stated by volume and the resin and hardener densities. Volume parts and weight parts are different numbers, so never swap the basis inside one chart.

What happens if I add too much hardener?

The mix can gel early, and the cured properties change; an amine-rich epoxy is not simply faster. Weigh to the chart and keep the batch inside its pot life.

Why do I need the base resin weight?

The parts ratio only sets proportions; the resin weight you draw sets the batch size. Enter the weight on your scale to get the hardener weight and the total batch.

Composites, Fiberglass & Advanced Materials calculator

Resin Mix Ratio Calculator

Scale a supplier mix chart in parts by weight to the resin weight you plan to draw. The hardener weight is the number to weigh; the ratio row confirms the chart you used.

What this calculator does

Hardener weight and total batch for a supplier mix chart given in parts by weight.

Formula used

Hardener required = base resin weight × hardener parts ÷ resin parts
Total mixed batch = base resin weight + hardener required
Resin to hardener ratio = resin parts ÷ hardener parts

Inputs explained

Resin Parts by Weight: Resin parts by weight from the supplier mix chart or datasheet.
Hardener Parts by Weight: Hardener parts by weight from the same supplier mix chart.
Base Resin Weight: Resin weight you plan to draw for the batch, from your scale.

How to use the result

Best suited to scaling a datasheet mix chart to a batch, weighing out an epoxy batch at the bench, checking a measured weigh-out against the chart.
A chart given by volume needs volume parts and densities, so do not enter it as weight. Pot life, mix temperature and degassing are set by the system, not by the ratio.

Current U.S. benchmarks

The producer price index for plastic resins and materials stands at 280.569 (BLS, Aug 2026), up 6.6% from a year earlier. Quotes priced off last quarter's material cost miss this move.
Steel mill PPI stands at 381.162 (BLS, Aug 2026), up 23.4% from a year earlier. New factory orders are up 8.5% year over year (Census).

Common questions

What does 100 to 28 by weight mean? For every 100 units of resin weight, add 28 units of hardener weight. Scale both by the same factor, so a 20 lb batch takes 5.6 lb of hardener.
Can I mix by volume instead of by weight? Only with a chart stated by volume and the resin and hardener densities. Volume parts and weight parts are different numbers, so never swap the basis inside one chart.
What happens if I add too much hardener? The mix can gel early, and the cured properties change; an amine-rich epoxy is not simply faster. Weigh to the chart and keep the batch inside its pot life.
Why do I need the base resin weight? The parts ratio only sets proportions; the resin weight you draw sets the batch size. Enter the weight on your scale to get the hardener weight and the total batch.

Last reviewed 2026-10-01.