Resin Calculator

Resin is measured by volume and mixed by ratio, so the calculation has two steps. First, the mould volume: a rectangular mould is length × width × depth; a cylinder is π × r² × depth; a full sphere is 4/3 × π × r³ and a dome is half that. In centimetres, the answer comes out in cm³, which equals millilitres. Multiply by the number of cavities and add a measured process allowance; the adjustable 10% default is only a starting estimate for material left in cups and on tools.

Second, the split. Epoxy comes in ratios like 1:1, 2:1, 3:1 or 100:33, and the product instructions should specify whether that ratio is by weight or by volume — the two are not interchangeable because the components can have different densities. Using the wrong basis can prevent a proper cure. This calculator shows the split only on the basis you select; use the one specified for that product.

Geometry covers regular shapes — box L × W × H, cylinder πr²h, sphere 4⁄3πr³, and a hemisphere half the sphere — with cubic centimetres equal to millilitres. For an irregular, water-compatible mould, fill to the intended line and weigh the water after subtracting the dry container: at ordinary room temperature, grams of water closely approximate millilitres. Empty and dry the mould completely before resin use, and do not use water when the mould or its release system forbids it.

One trap hides in that method: the water gives you a volume, not a resin weight. The calculator’s default mixed-density estimate is 1.15 g/ml, so it reports a 200 ml volume as approximately 230 g of mixed product. Treat that mass as a planning estimate and use the density on the product’s technical data sheet for an exact separate calculation; it is not a conversion between the Part A and Part B mixing ratios.

Part A and Part B can have different densities, so a product’s by-volume ratio is not automatically its by-weight ratio. Follow the exact basis and numbers on the label or technical data sheet: one 1:1-by-volume product may specify 1.2:1 by weight, while another chemistry uses different values. This calculator divides the required total on the basis you select; it does not infer the other basis from generic densities.

Use a suitable scale for a by-weight ratio and graduated containers or calibrated pumps for a by-volume ratio. Do not substitute one basis for the other. Follow the manufacturer’s minimum batch, mixing time, scraping, transfer and temperature guidance; those instructions are formulation-specific.

Epoxy cures exothermically: a larger mass retains more heat, which can cause bubbles, yellowing, cracks, smoke, container damage, or burns. Maximum depth is not a generic property of “epoxy”; it depends on the formulation, batch volume, mould geometry and ambient temperature. A coating resin and a deep-casting resin can have very different limits, so use the maximum pour volume and depth on the product’s current technical data sheet. The calculator’s depth field is volume arithmetic, not a safety approval.

If the product permits layered pours, use its stated recoat window and surface- preparation method; do not assume a universal number of hours or that sanding is always sufficient. Embeds must be dry, compatible and prepared according to the resin and mould instructions before they are enclosed.

Coverage divides volume by depth, and the metric version is beautifully simple: litres ÷ depth-in-mm = area in m² — one litre spreads one square metre at 1 mm thick, half a metre-squared at 2 mm. The table below converts to square feet for the common pour depths, including a US gallon for larger coat-and-seal jobs; divide your project’s area by these figures and buy the next bottle size up.

The calculator’s adjustable 10% default is a planning allowance for material left on the cup, stirrer and spout; it is not a product instruction. Measure losses from a small trial or use the manufacturer’s coverage guidance, then change the field to match the process. Avoid adding so much “just in case” that the batch exceeds a safe mix volume.

Match batch size to the product’s pot life and maximum mixed mass. Never return mixed material to either original container, and do not leave a large curing mass in a deep cup where heat can build rapidly. Wear the protective equipment named by the safety data sheet, ventilate as directed, and follow the manufacturer and local rules for leftovers and disposal.

A rectangular tray mould, 15 × 10 × 2 cm, in a 2:1 by-weight epoxy. Mould volume: 15 × 10 × 2 = 300 ml. With 10% mixing loss: 330 ml, which at 1.15 g/ml is 380 g of mixed resin. If the product specifies 2:1 by weight, part A = 380 × 2/3 = 253 g, part B = 127 g. Weigh A into a clean cup, add B, then follow that product’s mixing time, scraping, transfer and temperature instructions.

The same mould as a dome (say a 60 mm hemisphere for a paperweight): 2/3 × π × 3³ = 56.5 ml per dome — about a fifth of the tray. Small pours like that are where the 10% allowance matters most: 5 ml lost on a 56 ml pour is nearly 10% by itself.