Epoxy Mix Ratio Calculator
Split a total batch of epoxy into resin and hardener by any mix ratio — by weight or by volume — so every pour cures hard.
How it works
Resin = total × resin parts ÷ (resin + hardener) · Hardener = total × hardener parts ÷ (resin + hardener)
Two-part epoxy only cures correctly at the manufacturer's ratio: the hardener drives a chemical reaction that consumes the resin, so too little hardener leaves a soft tacky surface and too much leaves unreacted amine that weeps and yellows. The ratio is a proportion, so splitting a total batch means giving resin and hardener their fraction of the combined parts. Crucially, a ratio by weight is not the same as by volume because the two components have different densities — use the units your product specifies and measure precisely, since epoxy is unforgiving of eyeballing.
Worked example
For a 200 g batch at a 2:1 resin-to-hardener ratio, the combined parts are 3. Resin is 200 × 2 ÷ 3 = 133.3 g and hardener is 200 × 1 ÷ 3 = 66.7 g — a resin share of 66.7%.
Frequently asked questions
Can I just eyeball the ratio?
No. Epoxy cure is a stoichiometric reaction; being off by even 10–15% can leave it soft, sticky or brittle. Use a scale for weight-based products or graduated cups for volume-based ones.
Is the ratio the same by weight and volume?
Usually not. Resin and hardener have different densities, so a product that is 100:45 by weight might be 100:50 by volume. Always use the units printed on your specific product.
Does a bigger batch cure differently?
Yes — epoxy is exothermic, and a large mass in a deep cup traps heat, accelerating cure and risking overheating. For big pours use a wide shallow container or a slow hardener and pour in lifts.
Related calculators
This calculator is for educational purposes. Double-check important results before acting on them.