How is the split calculated?

The ratio parts are added together to get total parts. Part A is the A ratio divided by total parts, times the amount you need; part B is the B ratio divided by total parts, times the amount. For 2:1 mixing 12 oz, that is 8 oz A and 4 oz B.

Does it matter whether I mix by volume or by weight?

Yes, a lot. Resin and hardener usually have different densities, so a 2:1 by-volume ratio is not the same as 2:1 by weight. Always use the basis the manufacturer specifies, and set this tool to match.

What happens if I get the ratio wrong?

Off-ratio epoxy is the most common cause of a failed pour. Too much hardener or too much resin leaves the surface soft, tacky, or rubbery, and it may never fully cure. Measuring each part separately and accurately is essential.

Why measure each part separately instead of pouring to a total?

Because the ratio between the two parts is what cures the epoxy, not the total. Measure part A to its target, then part B to its target, rather than topping up one cup to a combined line, which hides ratio errors.

How long should I mix?

Most epoxies need thorough mixing for at least 3 minutes, scraping the sides and bottom of the container. Under-mixing leaves streaks and soft spots even when the ratio is perfect.

Resin & Epoxy Mixing Ratio Calculator

Get your epoxy ratio exact, every pour

Epoxy and casting resin only cure correctly when the two parts are combined in the right proportion. This calculator takes the mix ratio the manufacturer prints on the bottle and the total amount you want to make, then splits it into precise part A (resin) and part B (hardener) amounts — by volume or by weight.

How it works

A ratio like 2:1 means two parts resin to one part hardener, for three total parts. The math is a simple proportional split:

total parts = ratio A + ratio B
part A = (ratio A ÷ total parts) × total amount
part B = (ratio B ÷ total parts) × total amount

The basis matters: resin and hardener usually have different densities, so a 2:1 ratio by volume is not the same as 2:1 by weight. Set the tool to whichever basis your product specifies, and measure with a scale for weight ratios or graduated cups for volume.

Tips and example

You need 12 fluid ounces of a 2:1 by-volume epoxy:

Total parts = 2 + 1 = 3
Part A = (2 ÷ 3) × 12 = 8 oz resin
Part B = (1 ÷ 3) × 12 = 4 oz hardener

Always measure each part into its own container rather than topping one cup up to a combined line — that hides ratio errors. Mix slowly and thoroughly for at least three minutes, scraping the sides and bottom, then pour. Off-ratio epoxy is the number-one reason a pour stays tacky and never cures.