Get the ratio wrong and the pour never cures. This takes the ratio printed on your product's label — 1:1, 2:1, 100:45, anything — and a batch size, and tells you exactly how much part A and part B to measure, by volume or by weight.
Notes
Volume ratio and weight ratio are different numbers
Resin and hardener have different densities, so a 2:1 by volume product is NOT 2:1 by weight. Your data sheet states which one the printed ratio is, and usually gives both. Enter the ratio as your label states it, and pick the matching mode.
Weighing is more accurate
A scale reads to the gram; measuring cups trap film and misread menisci. If your data sheet gives the weight ratio, use it with a scale. If it only gives volume and you want to weigh, enter the specific gravity of each part from the data sheet and the tool converts.
Never adjust the ratio to change cure speed
More hardener does not cure faster — it leaves permanently soft resin. The ratio is chemistry, not seasoning. Change cure speed by changing product or temperature, never proportions.
Mix more than you pour
The film left on the bucket and stick is real: mix 5-10% extra. The batch size here should already include your waste allowance — the epoxy volume calculator on this site works that out.