Epoxy Resin Volume Calculator
Calculate how much epoxy resin your mold needs by shape and dimensions, add a waste allowance, and split it into Part A and Part B by mix ratio.
How it works
Rectangular = l×w×h · Cylinder = π·r²·h · Sphere = 4⁄3·π·r³ · Pyramid = ⅓·l×w×h · River table = l×w×h (void) · +waste% · 1 cm³ = 1 ml · Split A:B by mix ratio
Epoxy is mixed by combining two liquids, so you need to know both the total volume your mold will swallow and how to divide that between resin (Part A) and hardener (Part B). The total comes straight from geometry — the volume of a box, cylinder, sphere or pyramid in cubic centimetres, which equal millilitres one-for-one. Always mix a little extra: resin clings to the sides of the mixing cup and stir stick and a shortfall means a half-filled casting you cannot top up cleanly, so a 5–15% waste allowance is standard. The split follows the product's stated mix ratio: a 1:1 epoxy is half and half, while a 2:1 epoxy is two-thirds resin to one-third hardener. Getting that ratio right by volume is essential — off-ratio epoxy cures soft, sticky or not at all.
Worked example
A rectangular mold 20 × 10 × 3 cm has a volume of 600 cm³ = 600 ml. Adding a 10% waste allowance gives 660 ml to mix. With a 1:1 epoxy that is 330 ml of Part A and 330 ml of Part B; with a 2:1 epoxy it would be 440 ml of A and 220 ml of B.
Frequently asked questions
Why add a waste allowance?
Some epoxy always stays behind on the mixing cup, stir stick and any spillage, and you cannot cleanly add more once a pour has started to gel. Mixing 5–15% extra ensures the mold fills in one pour; leftover resin can be poured into a small mold or used for a test cure.
How do I handle a river table?
Calculate the full length × width × depth of the open channel to get the void volume, then subtract the volume of the wood slabs that sit inside it. What remains is the epoxy you actually need — this tool gives the void, so measure or estimate the displaced wood and take it off.
Does the mix ratio have to be exact?
Yes. Epoxy cures through a chemical reaction between resin and hardener, and an off-ratio mix cures soft, tacky or cloudy — it does not simply cure "a bit weaker." Measure Part A and Part B carefully by the ratio the manufacturer prints (by volume or weight as specified), not by eye.
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This calculator is for educational purposes. Double-check important results before acting on them.