Epoxy mix ratio calculator
Tell the tool how much mixed epoxy you need and your product's ratio, and get the exact resin and hardener amounts, batch by batch.
Enter your project
Optional: densities to convert between cups and grams
How it is calculated
A ratio like 2:1 means 3 equal parts in total: 2 of resin (Part A) and 1 of hardener (Part B). So Part A is the total x 2/3 and Part B the total x 1/3. For any ratio a:b, Part A = total x a / (a + b).
The ratio only works in the measure your label states. Resin and hardener have different densities, so 2:1 by volume is not 2:1 by weight. If you enter the density of each part from the data sheet (in grams per ml), the tool converts: grams = ml x density, and ml = grams / density.
Splitting into batches just divides both parts evenly. Smaller batches give you more working time, because mixed epoxy heats up faster in a full cup.
Worked example
You need 600 ml of a 2:1 by volume epoxy, mixed in 2 batches. Part A is 600 x 2/3 = 400 ml and Part B is 200 ml, so each batch is 200 ml + 100 ml.
With densities of 1.15 g/ml for the resin and 0.95 g/ml for the hardener, the same mix weighs 460 g + 190 g. That is 2.42 : 1 by weight, not 2 : 1, which is exactly why a volume ratio must never be measured on a scale.
Epoxy gets hot as it cures. Pouring deeper than your label allows can crack, cloud or yellow the resin, and very large masses can overheat. Work with good ventilation and nitrile gloves, and follow your product's safety data sheet.
Common questions
- How do I work out resin to hardener amounts?
- Add the two numbers of the ratio together, divide your total by that sum, then multiply by each number. For 300 ml of a 3:1 epoxy, 300 / 4 = 75, so 225 ml of resin and 75 ml of hardener.
- Can I measure a 2:1 epoxy on a scale?
- Only if the label says 2:1 by weight. Many products state 2:1 by volume and give a different weight ratio, such as 100:44. Using the volume ratio on a scale gives an off-ratio mix. Enter the densities here to get correct gram amounts.
- What happens if my epoxy mix ratio is off?
- It may stay soft, tacky or cloudy, or cure brittle, often in patches. Extra hardener does not make it cure faster or harder. If a small area stays sticky after the full cure time, it usually has to be scraped out and repoured.
- Where do I find the density of my resin and hardener?
- On the product's technical or safety data sheet, often listed as specific gravity. Specific gravity is the same number as density in g/ml. Many resins are around 1.1 to 1.2, and hardeners around 0.95 to 1.05.
- Is it better to mix epoxy by weight or volume?
- Weight is more accurate for small batches, because a few drops matter less on a scale than on a cup's markings. Either works if you use the ratio stated for that method. See the guide to weight vs volume.
Related tools and guides
WoodworkingCalc results are careful estimates. Products differ, so use the coverage, mix ratio and maximum pour depth printed on your own product label, and check the numbers against your project before you mix or buy.