Finishing calculator
Epoxy Mixing Ratio Calculator
Turn a 2:1, 3:1, 5:1, or custom ratio into actual amounts without changing the chemistry because the measuring cup looked close enough.
Sage’s guided lesson
The ratio is part of the formula, not a suggestion for adjusting cure speed
Sage will split the batch exactly. The resin and hardener still expect accurate measuring, thorough mixing, and a container that does not become an accidental hand warmer with ambitions.
Ratio parts describe proportions
A 2:1 mix contains three total parts
In a 2:1 ratio, Part A receives two of every three total parts and Part B receives one. In a 5:1 ratio, the total contains six parts.
The numbers do not identify ounces, grams, or milliliters by themselves. They only describe the relationship between the two components.
Copy the ratio and the measurement basis from the same manufacturer instruction. A ratio by weight may differ from the ratio by volume.
Add the ratio parts before dividing the batch
How to calculate any two-part mix
Known total batch
Part A = total × A parts ÷ (A parts + B parts)Part B = total × B parts ÷ (A parts + B parts)Worked example: 12 units at 2:1
Total ratio parts = 2 + 1 = 3Part A = 12 × 2 ÷ 3 = 8 unitsPart B = 12 × 1 ÷ 3 = 4 unitsIf one component amount is known, multiply by the opposite ratio part and divide by its own ratio part.
I know this is off topic, but this reminds me of a joke I heard when teaching this to one of my interns, Why did the melon jump into the lake? It wanted to be a watermelon. Yeah, I don’t see the connection either, but I think it is cute!
A fluid ounce and an ounce on a scale are different measurements
Density decides whether weight and volume ratios match
Volume compares space. Weight or mass compares how much matter is present. Resin and hardener often have different densities, so a 2:1 volume ratio may not be a 2:1 weight ratio.
Graduated cups are appropriate only when the product specifies volume mixing. A suitable scale is appropriate only when the product supplies a weight ratio and the scale can resolve the required amount.
Use the manufacturer’s published alternate ratio or density data. “They are both liquids” is not a conversion factor.
Small batches magnify small measuring errors
Accuracy includes mixing, not just dispensing
A one gram error is minor in a 500 gram batch and enormous in a 5 gram batch. Choose a batch size large enough to measure accurately but small enough to use within the working time.
- Use clean dedicated tools.
- Scrape the sides, bottom, and corners while mixing.
- Transfer to a second clean cup and mix again when the product procedure recommends double-cup mixing.
- Do not scrape unmixed residue from the first cup onto the project.
Colored streaks, soft spots, or sticky areas often come from inaccurate ratio or incomplete mixing.
Pot life measures a contained mass, not every possible working condition
The cup and the coating can cure at different speeds
Two-part epoxy systems became important industrial materials in the twentieth century because resin and hardener could be stored separately, then reacted when needed.
Pot life is normally measured for a specified quantity in a specified container and temperature. The same mixture spread into a thin film can remain workable longer because heat escapes more easily.
Larger batches retain reaction heat, which accelerates cure and produces still more heat. This feedback is called exotherm.
A fast-curing cup does not mean the thin film on the project has reached full cure. Pot life, working time, recoat time, and final cure are different milestones.
Changing the ratio does not create a custom hardener speed
It usually creates uncured chemistry
Do not add extra hardener to make epoxy cure faster or extra resin to slow it down. The intended ratio supplies the chemical groups needed for the reaction; excess component can remain unreacted.
- Use the recommended hardener or product for the desired cure speed.
- Observe minimum and maximum application temperatures.
- Control batch size and container geometry to manage exotherm.
- Wear the protective equipment and use the ventilation listed in the safety data sheet.
The calculator only divides amounts. It does not confirm product compatibility, cure schedule, induction time, filler loading, or safe batch mass.
And that is the lesson properly accounted for
The ratio is exact, the cup was scraped, and the batch remains pleasantly unexciting
You now know how to split any two-part ratio, why weight and volume cannot be swapped casually, and why changing hardener quantity is chemistry vandalism. Sage has mixed the cheese fries 2:1, although nobody is certain what the second component was.
Quick answers
Epoxy Mixing Ratio Calculator questions
Does 2:1 mean two ounces and one ounce?
Only if the product specifies that ratio by volume and ounces are the chosen volume unit. The ratio may instead be by weight.
Can I use the same ratio by weight and volume?
Not unless the manufacturer says so. Different component densities usually make the ratios different.
Can I add extra hardener to speed the cure?
No. Altering the specified ratio can leave unreacted material and cause weak, sticky, or uncured epoxy.
Why did a large batch get hot so quickly?
Epoxy cure releases heat. A large contained mass retains heat and accelerates its own reaction.
What is the difference between pot life and working time?
Pot life is measured for a specified mass in a container. Open working time on a project can differ because heat dissipates differently.
Why use a second mixing cup?
Transferring and remixing reduces the chance that unmixed material from the sides and bottom reaches the project.
How small a batch can I mix?
Only as small as your tools can measure accurately. Very small batches can have large percentage errors.
Before you use the result
Follow the product label and safety data sheet. Incorrect ratios and large contained batches can produce uncured material, excessive heat, smoke, burns, or fire.