Resin Mold Calculator

Every resin brand ships a calculator that assumes you're buying their resin. This one isn't selling anything: pick the mold shape, type its dimensions in millimeters or inches, and read the total with a waste allowance baked in — then the exact Part A and Part B pours for a 1:1, 2:1, or 3:1 ratio. Coasters, deep-pour molds, domes, or a mold whose volume you already know in milliliters: same three seconds.

The waste number matters more than people expect. Resin clings to the cup wall and the stir stick, textured molds hold more than their nominal volume, and mixing a second micro-batch mid-pour is how streaks and soft spots happen. Eight percent is a sane default; go higher for texture and embeds.

Questions this tool gets asked

How do I calculate how much resin a mold needs?

Compute the mold cavity's volume, then add a waste allowance. A rectangular mold is length × width × depth; a cylinder is π × (diameter ÷ 2)² × depth; a hemisphere is two-thirds × π × (diameter ÷ 2)³. Divide cubic millimeters by 1,000 for milliliters. This calculator does the geometry, adds your waste percentage, and splits the total into Part A and Part B.

How much extra resin should I mix?

Mix 5–10% extra for simple molds, and up to 15% for pieces with texture, deep corners, or when you're drizzling over the top. The extra covers what clings to the mixing cup and stir stick, and running short mid-pour is far more expensive than a little cured waste.

Is the mix ratio by volume or by weight?

This calculator splits by volume, which is how most art and craft epoxies are labeled (1:1, 2:1). Some resins — especially polyurethanes and industrial epoxies — specify ratios by weight, and Part A and B densities differ, so the two are not interchangeable. Check your bottle: if it says "by weight", use a scale and the manufacturer's gram ratio instead.

Why did my resin overflow the mold?

Usually one of three things: the waste allowance went into the mold instead of staying in the cup, embedded objects displaced their own volume of resin, or a flexible silicone mold bulged under the pour. If you're embedding items, subtract a rough estimate of their volume, and pour in stages for deep molds.

Does anything I enter leave my browser?

No. The geometry runs in this tab, your entries are remembered in this browser's local storage only, and the page works offline once loaded. Nothing is uploaded.

How much resin do I need for one coaster?

A standard 4-inch (100 mm) round coaster mold at 8 mm deep holds about 63 ml; add 8–10% waste and mix roughly 68–70 ml — about 35 ml each of Part A and B at 1:1. Guides quote anything from 60 to 100 ml because molds differ in depth more than people expect: at 10 mm deep the same coaster needs ~79 ml. Enter your mold's real diameter and depth above for the exact split.

How many coasters can I make from 1 liter of resin?

Around 13–14 standard 4-inch coasters at 8 mm deep from a 1 L kit (A+B combined), once you include mixing waste — call it a dozen to be safe, or 3 full sets of four. Deep-pour 10 mm molds drop that to about 11. Compute one coaster above, then divide your kit size by the 'mix this much' figure.

Why is my resin still bendy after curing?

Three causes cover nearly every bendy pour: an off-ratio mix (the reason to measure A and B precisely — use the split above rather than eyeballing), under-mixing (scrape cup walls for a full 3 minutes), and a cold room — most epoxies want 21–24°C and stay soft for days below that. Thin pieces also flex until full cure at 72 hours. If it is still rubbery after a warm week, the ratio was off; there is no fixing it — remake.

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