How much epoxy resin do you need?

Resin is just volume

The amount of epoxy you need is the volume you're filling: length × width × depth for anything rectangular, and π × radius² × depth for anything round. Work in inches and you get cubic inches; one cubic inch is 16.39 ml, or about 0.55 fl oz.

Then add about 10% for what stays in the mixing cup and what drips over edges. Open the Resin Calculator to do the sums and split the total into Part A and Part B.

Worked examples

Four round coasters, 4 inches across and 1/4 inch deep:

• One coaster: π × 2² × 0.25 = 3.14 cubic inches.
• Four coasters: 12.6 cubic inches, which is 206 ml or 7.0 fl oz.
• With 10% extra: 7.7 fl oz to mix. At a 1:1 ratio, that's about 3.8 fl oz each of Part A and Part B.

A tabletop seal coat, 3 × 6 feet at 1/8 inch:

• 72 × 36 × 0.125 = 324 cubic inches: about 180 fl oz, or 1.4 gallons.
• With 10% extra, about 197 fl oz (1.54 gallons).
• Each square foot of a 1/8 inch coat takes about 10 fl oz (295 ml).

A river table, 6 feet long, a river averaging 6 inches wide, 1 1/2 inches deep:

• 72 × 6 × 1.5 = 648 cubic inches: 10.6 litres, or 2.8 gallons.
• With 10% extra, 3.1 gallons. That's roughly 13 kg of mixed resin, so check the kit sizes before you order.

Odd shapes: measure with water

For a mold that isn't a simple shape (a pendant, a tray with curved walls, a letter), fill it with water to where the resin will reach. Pour the water into a measuring jug, or weigh it: 1 gram of water is 1 ml. Choose Measure with water in the calculator and enter the amount. Dry the mold completely before pouring resin, because water ruins the cure.

Why deep pours need layers

Epoxy gives off heat as it cures, and the thicker the pour, the hotter it gets. Too much at once can overheat, crack, yellow or trap bubbles.

• Coating or tabletop epoxy is usually made for about 1/8 inch (3 mm) per coat.
• Deep pour or casting epoxy handles 1 to 2 inches (2.5–5 cm) or more per pour.

The river table above fits in one 2 inch pour of deep pour resin, but needs two pours if your resin's limit is 1 inch. Always use your product's own maximum and wait the time it gives between layers.

Volume ratio or weight ratio?

Use whichever your resin's label gives. Ratios like 1:1 and 2:1 are usually by volume, measured in marked cups. Ratios like 100:45 are by weight, measured on a scale. The two parts have different densities, so measuring a volume ratio on a scale, or a weight ratio in cups, mixes it wrong and it may stay soft or sticky.

For weight ratios, the calculator turns the volume into grams using the mixed resin's density, about 1.1 g/ml for most epoxy. Check your resin's data sheet for its exact figure.

Work out your pour, step by step

1. Choose the Shape and enter its measurements and Pour depth. Fractions like 1/8 work.
2. Enter How many pieces you're pouring.
3. Choose the Resin type and check the Maximum depth per pour against the label.
4. Pick the Mix ratio (A:B) from your resin's instructions.
5. Read Resin to mix, the Part A and Part B amounts and the number of pours.

Mix only what you can pour within the resin's working time. For a big project, mixing two or three smaller batches is safer than one huge one.