Epoxy Resin Ratios Explained: 1:1 vs 2:1 (and Why It Matters)
The ratio on the bottle is the single most important number in resin, and it’s also the one people most often get wrong — usually because they assume every resin works the way their last one did. It doesn’t. Mix a 2:1 resin like a 1:1, and you’ve got a cup of expensive goo that will never harden.
So let me actually explain what these numbers mean, why brands differ, and the one trap that catches almost everyone at least once.
What the ratio is really telling you
Epoxy is a reaction between two parts — resin (Part A) and hardener (Part B). The ratio tells you how much of each to combine so that every resin molecule has exactly the hardener it needs to cure. It’s chemistry, not a suggestion, and there’s very little wiggle room.
A 1:1 resin means equal amounts of A and B. A 2:1 means two parts resin to one part hardener. Both are completely normal — they’re just different formulas engineered to cure correctly at those proportions. Neither is “better.” What matters is matching the number to the bottle in your hand.
The trap nobody warns you about: by volume vs by weight
This is the one that got me, and it gets a lot of people.
Some resins state their ratio by volume (measure with marked cups) and some state it by weight (measure on a scale). Here’s the catch: resin and hardener don’t weigh the same per unit of volume. So a resin that’s 1:1 by volume is often not 1:1 by weight — the weight ratio might be something like 100:90. If you grab a scale and weigh out a “1:1” resin that was meant to be measured by volume, you can throw the mix off without realizing it.
Rule of thumb that keeps you safe: measure the way the bottle tells you to. If it gives a volume ratio, use graduated cups. If it gives a weight ratio, use a scale and use their exact numbers. Don’t convert one to the other in your head.
I lost a batch of six pendants to exactly this once — switched brands, kept my old muscle memory, mixed a 2:1 system at 1:1. Two days waiting, still soft. Never hardened. Now I read the bottle out loud before I open it. Slightly ridiculous, totally worth it.
Does a little off-ratio matter?
Yes, more than you’d hope. Epoxy isn’t forgiving like baking, where a bit extra leavening still works.
Too much hardener doesn’t cure it “harder” — it leaves unreacted hardener in the mix, which stays soft, can get rubbery, and sometimes weeps an oily film. Too little hardener leaves resin with nothing to react with, so it stays tacky. Either direction lands you in the same place: a piece that won’t fully set. For the deeper version of what goes wrong, I wrote about mixing mistakes here.
So aim for accurate, not approximate. Small jewelry batches are less forgiving than big ones, because when you’re mixing 20 grams total, being half a gram off is a real percentage of the whole.
How to hit the ratio every time
For volume-ratio resins, use straight-sided graduated mixing cups and read the lines at eye level — angled cups and a glance from above will lie to you. For weight-ratio resins, a cheap kitchen scale that reads to 0.1 g is plenty; tare the cup, pour Part A to your target, tare again, add Part B to its number.
And whichever you use, mix thoroughly afterward — correct ratio plus lazy stirring still gives soft spots, because the mix has to be complete everywhere, not just close.
One last thing: don’t try to “fix” a curing piece by adding more hardener on top. It doesn’t work — the reaction’s already going, and you’ll just make a second mess. If the ratio was wrong, the move is to start over with a fresh, correct batch.
Browse my handmade silicone molds for resin.
Not sure whether your resin is measured by volume or weight? Tell me the brand and what the label says, and I’ll help you read it right before you pour.
— Nikolai