Epoxy Mix Ratio Calculator

Introduction to epoxy resin and hardener mix ratios

An epoxy system reaches its intended strength only when resin, usually called Part A, and hardener, usually called Part B, are combined in the proportion specified by the manufacturer. That proportion is the epoxy mix ratio. It may be written as 1:1, 2:1, 5:1 or as a hundred-based ratio such as 100:45. The first number belongs to resin and the second to hardener.

Unlike thinning paint, adjusting an epoxy ratio is not a useful way to change cure speed. Resin and hardener take part in a chemical reaction, so adding extra hardener can leave both unreacted hardener and unmatched resin in the cured film. The result may remain soft, rubbery or tacky even after warming or waiting longer.

The measuring basis matters just as much as the numbers. A 2:1 ratio by volume does not generally mean 2:1 on a scale because resin and hardener rarely have identical densities. Many liquid resins are around 1.10–1.20 g/cm³, while many hardeners are around 0.95–1.05 g/cm³. This calculator uses each component’s density to preserve the actual formulation while converting between mass and volume.

The calculator splits a desired total into resin and hardener, reports both components in grams and millilitres, and adds a planning allowance for material left on the cup, stir stick or substrate. It also reports the equivalent ratio on the other measuring basis, providing a useful check against a technical datasheet.

How to use this epoxy batch calculator

Begin with the product label or technical datasheet rather than a ratio remembered from another brand. Enter the resin and hardener parts exactly as published. For a 5:1 system, enter 5 for resin and 1 for hardener. For a 100:45 industrial formulation, enter 100 and 45 without simplifying unless you want to.

1. Choose whether the published ratio is stated by weight or volume. This determines what the ratio numbers represent.
2. Enter the amount of mixed epoxy required and select its unit. The calculator accepts grams, kilograms, ounces, pounds, millilitres, litres and US fluid ounces.
3. Enter resin and hardener densities in g/cm³. A datasheet may label these values “density” or “specific gravity.” For ordinary liquids, the numerical value of specific gravity is used the same way here.
4. Add a waste allowance. Three to ten percent is common, although a very small batch or absorbent reinforcement may require careful testing.
5. Select Calculate mix, then measure the displayed resin and hardener quantities with an instrument suitable for the selected basis.

A scale is often more repeatable for small batches, but it is only appropriate when you use the ratio by weight. Graduated cups and syringes are suitable for a ratio by volume. Never put volume-ratio numbers directly on a scale unless the manufacturer explicitly says that both ratios are the same.

The epoxy mix formulas for mass, volume and density

When a resin-to-hardener ratio is stated by weight, the resin mass fraction and component masses are:

Here, is total mixed mass. When the ratio is stated by volume, each part must first be related to mass through its density:

The component volumes follow by dividing mass by density. The mixed density is the total mass divided by the sum of those component volumes:

The allowance is applied to the requested total before the split:

The equivalent volume ratio can be obtained from the weight ratio by accounting for the two densities:

Worked example: 900 mL of 2:1 laminating epoxy

Suppose a laminating epoxy is specified as 2:1 by volume. Its resin density is 1.16 g/cm³, its hardener density is 1.00 g/cm³, and the job needs 900 mL. A 5% waste allowance raises the amount to be mixed to 945 mL.

The volume ratio allocates 630 mL to resin and 315 mL to hardener. Those volumes weigh 730.8 g and 315.0 g respectively, producing a total batch mass of about 1045.8 g. Although the volume ratio is exactly 2:1, the corresponding weight ratio is 730.8:315, or approximately 2.32:1. In hundred-based form, that is about 100:43.1 by weight.

This example shows why the basis selector cannot be ignored. Weighing the two components at 2:1 would produce a different hardener fraction from pouring them at 2:1. The calculator’s equivalent-ratio lines make that difference visible before material is committed.

Common epoxy ratio patterns and measuring choices

Craft and repair epoxies are frequently supplied at 1:1 or 2:1 by volume because those proportions are convenient for paired pumps and marked cups. Marine laminating systems may use 5:1, while industrial adhesives and casting products are often specified by weight per hundred parts of resin. None of these conventions identifies a universal chemistry; the product instructions remain authoritative.

Pot life, exotherm and the Pot Life Race game

Correct proportions do not guarantee unlimited working time. Epoxy curing is exothermic: the reaction releases heat, and a warmer mixture reacts faster. A deep batch in a narrow cup has relatively little cooling area for its mass, so its temperature can rise rapidly. The same material spread as a thin film has more effective cooling area and usually remains workable longer.

This rule-of-thumb expression represents pot life roughly halving for each 10 °C increase. It is not a replacement for a product datasheet, because formulation, batch mass and test geometry matter. It does explain why mixing a smaller batch or transferring epoxy to a shallow tray can be safer than leaving a large quantity in a tall cup.

The optional Pot Life Race below turns those ideas into a short balancing challenge. Match the specified measuring basis, choose a batch and container, then pour before heat and cure consume the available pot life. Missions introduce hotter shops, faster hardeners and deeper pours. The game is educational and does not alter the calculator result.

Interpreting resin, hardener and total results

The result panel reports each component as both mass and volume. When weighing, tare the container before adding resin. You may tare again before adding hardener, or add hardener until the scale reaches the displayed combined mass. When measuring by volume, use a clean graduated cup or syringe and read the liquid level consistently.

Mixed density connects the mass and volume views. The equivalent ratio shows how the same formulation appears on the other basis. If a datasheet publishes both weight and volume ratios, compare them with the calculated values. A substantial disagreement usually means a density, ratio number or basis was entered incorrectly.

Limitations, assumptions and epoxy handling safety

The calculation assumes that component volumes are additive. Real mixtures can contract or expand slightly, but that effect is generally smaller than ordinary cup-reading error. Densities also vary with temperature and product batch. Use current manufacturer data when precision matters.

• Fillers, pigments, fibres and solvents are not included. Add approved fillers only after resin and hardener have been proportioned and mixed as directed.
• The waste percentage is a planning allowance, not permission to make a dangerously large batch.
• Pot-life behaviour in the game is illustrative. Follow the manufacturer’s maximum batch size, pour depth and temperature limits.
• Manufacturer instructions and the safety data sheet take priority over this calculator.

Wear nitrile gloves and eye protection, provide suitable ventilation, and avoid skin contact with uncured resin or hardener. Repeated exposure can cause sensitisation. If a batch begins smoking or heating uncontrollably, stop handling it, keep people away and follow the product’s emergency guidance. Do not seal a reacting batch in a container.

Epoxy mixing frequently asked questions

Sources: Ratio conversion follows the density method described by Meridian Adhesives Group. Measuring guidance is consistent with TotalBoat and WEST SYSTEM. Exotherm discussion references Gougeon Brothers’ guidance on controlling epoxy exotherm. Last reviewed August 2026.