Resin Mold Volume & Mix Split Calculator

How to Calculate Epoxy Resin Volume and Weight Ratios

Casting epoxy resin requires exact chemical proportions. Unlike simple water or solvent mixtures, epoxy is a thermosetting polymer. When Part A (resin) and Part B (hardener) mix, they undergo a covalent cross-linking chemical reaction. Incorrect ratios leave unreacted monomer molecules suspended in the matrix, leading to sticky, rubbery casts, bubbles, or cloudy layers.

To calculate the exact weight of resin needed, you must follow three fundamental physical stages: volume determination, density scaling, and ratio division.

1. Geometric Volume Calculation

First, calculate the volume of your mold cavity. Standard shapes use classical geometric formulas:

• Rectangular Molds (Trays, Coasters): Length × Width × Depth
• Cylinder Molds (Tumblers, Jars): π × (Diameter / 2)² × Depth
• Sphere Molds (Orbs, Paperweights): (4/3) × π × (Diameter / 2)³

Always measure in centimeters to ensure compatibility with metric densities, as 1 cubic centimeter (cm³) is exactly equal to 1 milliliter (ml).

2. Density Conversion

Water has a density of 1.00 grams per milliliter, but liquid epoxy resins are denser. The specific gravity of standard epoxy ranges between 1.10 and 1.15 g/ml depending on the brand. This means if your mold has a volume of 100 ml, you actually need 110 to 115 grams of liquid resin. Failing to account for density results in under-filling your mold cavity.

Total Weight (grams) = Volume (ml) × Density (g/ml) × (1 + Waste Factor / 100)

3. Mix Ratio Weight Splits

Resin systems are specified as ratio by volume (typically 1:1 or 2:1) or by weight. If splitting by volume but using a scale (which is highly recommended for accuracy), you must check the technical datasheet (TDS). For most 1:1 volume epoxy systems, the density of Part A is slightly higher than Part B, allowing a direct 1:1 weight split as a close approximation. For 2:1 systems:

• Part B (Hardener) Weight: Total Weight / 3
• Part A (Resin) Weight: (Total Weight / 3) × 2

Use our interactive calculator to automate these calculations and scale your recipe for a zero-waste pouring experience.