Epoxy Resin to Hardener Mix Ratio Converter

Epoxy systems consist of two components — resin and hardener — that must be mixed in a precise ratio for proper curing. The ratio can be specified by weight or by volume, and these are not always the same because resin and hardener have different densities.

Common epoxy mix ratios:

1:1 Ratio (equal parts): Found in many consumer adhesives like 5-minute epoxy and structural adhesives. This ratio is the easiest to measure because you simply use equal amounts of each component. Most 1:1 epoxies measure the same by both weight and volume because the components are formulated to have similar densities.

2:1 Ratio (2 parts resin to 1 part hardener by volume): The most common ratio for table-top epoxy, bar-top coatings, and deep-pour casting resins. By weight, a 2:1 volume ratio often works out to approximately 100:45 or 100:47 because hardeners are typically denser than resins. Always check the manufacturer’s technical data sheet for exact weight ratios.

3:1 Ratio: Common in marine epoxies and some laminating systems. These systems offer longer working times and lower exothermic heat, making them suitable for large layups and thick applications.

5:1 Ratio: Found in some industrial and marine epoxy systems. The higher resin proportion gives a longer pot life but requires very accurate measurement since small errors in the hardener amount have a proportionally larger effect.

Why accuracy matters: Under-mixing (too little hardener) results in a soft, tacky cure that never fully hardens. Over-mixing (too much hardener) can cause brittleness, discoloration, or excessive heat generation during curing. Most manufacturers recommend staying within plus or minus 5% of the specified ratio by weight.

Measuring by weight vs volume: Weight measurement is more accurate because liquid volumes can be affected by air bubbles, meniscus reading errors, and temperature-related density changes. Professional epoxy users always measure by weight using a digital scale accurate to at least 1 gram. For small batches, a scale accurate to 0.1 grams is recommended.

Working time (pot life): After mixing, epoxy begins to react and generate heat. The usable working time depends on the batch size (larger batches cure faster due to heat buildup), ambient temperature (warmer = faster cure), and formulation. Typical pot lives range from 5 minutes for fast adhesives to 45 minutes or more for coating systems. Spreading epoxy into a thin film extends the working time because heat dissipates more easily.

Temperature considerations: Most epoxies should be mixed and applied at 60-85F (16-29C). Below 60F, the reaction slows dramatically and may not cure fully. Above 85F, pot life shortens and the risk of exothermic overheating increases. Some specialty epoxies are formulated for low-temperature cure (down to 35F or 2C).