Resin Mixing Calculator
Work out exactly how much resin and hardener to mix, at your product's own ratio — by volume for a pour of a given size, or by weight for a target batch.
Measurement basis
Mix ratio (resin : hardener)
Bar shows resin and hardener proportional to their amount in the mix.
Temperature, cure, and common mistakes
- The mix ratio itself never changes with temperature — it's fixed by the chemistry, and changing it breaks the cure. What temperature DOES change is pot life: as a rough rule of thumb, working time roughly halves for every ~10°C (~18°F) rise above room temperature, and roughly doubles for the same drop.
- Never eyeball the ratio, even "close enough." A small ratio error reliably leaves a permanently soft, tacky mix that will never fully cure — measure precisely, whichever basis your product specifies.
- Mix thoroughly, scraping the sides and bottom of the container repeatedly — pockets of unmixed hardener along the edges are a common cause of soft spots.
- High humidity can cause amine blush — a greasy film that dulls gloss and blocks recoating. Work below about 80% relative humidity, ideally closer to 50%.
- Standard (non-deep-pour) resin is generally safe up to about 0.6 cm per layer; dedicated deep-pour formulas are rated up to roughly 1-5 cm. Pouring thicker than your product allows lets heat build up faster than it can escape, risking cracking, yellowing, or clouding.
How this is calculated
For a volume pour, the tool multiplies your surface area by the pour thickness to get the total mix volume — in centimetres, that's exact: 1 cm³ equals 1 ml by definition, so no rounding or brand-specific conversion is involved. A weight-basis mix skips geometry entirely and starts from the total weight you enter. Either way, a buffer percentage is added for mixing loss and spillage, and the result is split into resin and hardener using your product's own ratio.
Common questions
Why doesn't this calculator convert between a volume ratio and a weight ratio?
Because there's no reliable constant to convert with. Checking real published data sheets, a 1:1-by-volume system typically works out to roughly 100:83-84 by weight (hardener is lighter), but a 5:1-by-volume system (West System 105/205) is only about 5:1.19 by weight — the density gap between resin and hardener varies a lot by formulation. Guessing a conversion would silently give you the wrong amounts, so instead you enter the ratio exactly as your product's label states it — by volume or by weight — and the result comes out in that same basis.
My product's ratio isn't one of the preset buttons — can I still use it?
Yes. The preset buttons (1:1 through 5:1) just fill in the two ratio fields as a shortcut for the most common products — both fields stay fully editable, so an odd ratio like 100:83 or 120:100 (both real, published ratios) works exactly the same way.
What happens if I get the ratio slightly wrong?
Epoxy cures through a fixed chemical reaction between resin and hardener — it isn't like paint that just dries. Too much or too little hardener leaves unreacted material behind, which usually shows up as a permanently soft, tacky, or sticky surface that never fully hardens, sometimes not until days later. Precise measuring matters more than most other resin variables.
Part of Hobby & Craft Calculators