Epoxy Mixing Ratios Explained: Getting Part A:B Exactly Right
Volume ratio and weight ratio are never the same number for a given product — mixing up the two is one of the most common, most avoidable cure failures.
A mix ratio like 2:1 means two parts resin (Part A) to one part hardener (Part B) — but that number only means something once you know whether it’s by volume or by weight. Resin and hardener have different densities, so the same product can be 2:1 by volume and a completely different ratio by weight. The Resin Mixing Ratio Calculator does the volume math for any batch size once you know your product’s ratio.
How to read the inputs
Mix Ratio (Part A : Part B)
- Enter the exact ratio from your product’s TDS — presets are provided for common ratios like 1:1, 2:1, 3:1, and 4:1
Total to Mix
- Your full batch or kit size, in whichever unit your product is sold in (L, mL, gal, or kg)
Part A / Part B
- The exact amount of each component to measure out for that batch size, plus each one’s share as a percentage
Unit toggle
- Switch between liters, milliliters, gallons, and kilograms depending on how your product is labeled
Worked example
A product rated at a 2:1 ratio by volume, mixing a 3 gal batch: total parts = 2 + 1 = 3, so each part is 3 ÷ 3 = 1 gal. Part A (2 parts) = 2.00 gal, and Part B (1 part) = 1.00 gal. If that same product’s TDS instead listed a weight ratio — say 100:83 — those figures would be different, because resin and hardener don’t weigh the same per gallon. Always confirm which basis the number on the label actually refers to.
Try it with your own ratio
Enter your product's Part A:B ratio and total batch size — the split updates instantly.
Full result gives exact Part A and Part B volumes for any batch size.
Open the live calculator →Common mistakes
- Assuming volume ratio and weight ratio are the same number — they almost never are, since Part A and Part B have different densities
- Adding extra hardener to try to speed up the cure — it doesn’t work, and causes yellowing and a weaker film instead
- Not scraping the sides and bottom of the mixing container, leaving unmixed resin that shows up as soft spots later
- Eyeballing a ratio instead of measuring precisely — even a small error compounds across a full batch
Frequently Asked Questions
Is a 2:1 ratio by volume the same as 2:1 by weight?
No, almost never. Resin and hardener have different densities, so a product with a 2:1 ratio by volume might be closer to 100:83 by weight. Always check which basis your product’s TDS actually specifies before measuring — the two are not interchangeable.
What happens if I add a little extra hardener to speed up the cure?
It backfires. Excess hardener doesn’t cure faster — it leaves unreacted amine in the film, which can cause amber discoloration, a brittle or weak surface, and a higher risk of blushing. It never speeds up the working cure the way people assume.
Why is my epoxy still soft or tacky after mixing to the correct ratio?
The most common cause with a correct ratio is incomplete mixing — resin left unmixed along the sides or bottom of the container. Scrape the walls and base of the pot while mixing, then switch to a clean container and mix again briefly (a "double bucket" mix) before pouring.
Should I measure by volume or by weight?
Weight, using a digital scale, is more accurate for larger or more sensitive batches, since it accounts for the density difference directly. Volume measurement is faster and fine for most standard coating work. Either is acceptable as long as you use the ratio your product actually specifies for that method.