Is epoxy mix ratio by volume or by weight?

Most consumer epoxies specify ratios by volume (most common). Some industrial or marine systems specify by weight. Always check your product's datasheet — mixing by volume when weight is required (or vice versa) results in uncured epoxy.

Which mix ratio is best — 1:1 or 2:1?

Neither is universally 'better' — it depends on the product formulation. 1:1 is easier to measure. 2:1 systems often offer higher hardness and better heat resistance. Always use the ratio specified by your resin manufacturer.

Epoxy Mix Ratio Calculator

Q: What does a 2:1 epoxy mix ratio mean?

A 2:1 ratio means 2 parts resin (Part A) to 1 part hardener (Part B) by volume. For every 2 oz of resin, add 1 oz of hardener. Total batch = 3 oz. Part A makes up 66.7% of the mix.

Q: How do I calculate Part A and Part B for a 2:1 ratio?

For a 2:1 ratio: Part A = (total volume × 2) ÷ 3. Part B = total volume ÷ 3. Example: 30 fl oz total → Part A = 20 oz, Part B = 10 oz.

Q: What happens if my epoxy mix ratio is slightly off?

Small deviations (within 2–3%) may reduce hardness or increase cure time but the epoxy will still cure. Larger errors (10%+) can result in permanently sticky, soft, or brittle epoxy that won't cure correctly. Always measure accurately.

Getting the mix ratio right is the single most important step in any epoxy project. An off-ratio mix — too much hardener or too little — results in epoxy that stays permanently tacky, cures too soft, or never cures at all. This page explains how every common ratio works, how to calculate exact Part A and Part B amounts, and includes a quick inline calculator. For full project volume and cost estimates, use the main epoxy calculator.

Need Part A and Part B amounts for your whole project? The full calculator handles volume, mix ratio, and cost in one step.

⚗️ Open Full Epoxy Calculator ⟶

🧮 Quick Mix Ratio Calculator

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⚗️ How Mix Ratios Work

Understanding Epoxy Mix Ratios

An epoxy mix ratio describes the proportion of Part A (resin) to Part B (hardener) needed for the chemical curing reaction to complete correctly. The ratio is either by volume or by weight — the two are not interchangeable.

The ratio is always written as A:B. A "2:1 ratio" means 2 parts resin for every 1 part hardener. The total batch is 3 parts — resin makes up 66.7% and hardener makes up 33.3%.

1:1 Equal volumes of resin and hardener 50% / 50%

2:1 2 parts resin, 1 part hardener 66.7% / 33.3%

3:1 3 parts resin, 1 part hardener 75% / 25%

4:1 4 parts resin, 1 part hardener 80% / 20%

📐 Calculation Formulas

How to Calculate Part A and Part B

Given a total batch size and a ratio of A:B, calculate each part:

Part A = Total × A ÷ (A + B) Part B = Total × B ÷ (A + B)

Example — 2:1 ratio, 30 fl oz total:

Part A = 30 × 2 ÷ (2+1) = 30 × 0.667 = 20.0 fl oz Part B = 30 × 1 ÷ (2+1) = 30 × 0.333 = 10.0 fl oz

Example — 1:1 ratio, 24 fl oz total:

Part A = 24 × 1 ÷ (1+1) = 12.0 fl oz Part B = 24 × 1 ÷ (1+1) = 12.0 fl oz

⚖️ By Volume vs By Weight

Mix Ratio by Volume vs by Weight — What's the Difference?

Most consumer epoxies specify ratios by volume — meaning you measure using graduated cups, syringes, or pump dispensers. This is the most practical method for DIY projects.

Some industrial, marine, or high-performance systems specify ratios by weight. Because Part A and Part B have different densities, a 2:1 ratio by volume becomes a different ratio by weight (typically around 100:43 or 100:45 by weight for a 2:1 volume ratio).

Critical rule: Never mix up the two. If your datasheet says "2:1 by volume" and you measure by weight using the same ratio, your epoxy will not cure correctly. Check your product label or technical datasheet — it will specify "by volume" or "by weight" explicitly.

Ratio (by volume)	Approximate ratio by weight*	Common applications
1:1	~100:83 to 100:90	Casting, tabletop, jewelry
2:1	~100:43 to 100:46	River tables, floor coatings
3:1	~100:29 to 100:32	Marine, structural laminates
4:1	~100:22 to 100:25	High-performance coatings

*Exact weight ratios vary by product formulation. Always use your manufacturer's datasheet.

💡 Common Mistakes

Mix Ratio Mistakes to Avoid

Estimating by eye — Never eyeball the ratio. Use graduated measuring cups, a digital scale, or pump systems calibrated to your ratio.
Mixing volume and weight ratios — If the label says "by weight," use a scale. If it says "by volume," use measuring cups. Don't mix methods.
Counting pump strokes on an uncalibrated dispenser — Verify your pump output with measuring cups before trusting it for large pours.
Not scraping the mixing cup sides — Unmixed resin or hardener clinging to the cup sides goes into your pour and creates uncured spots.
Mixing too fast — Aggressive mixing introduces air bubbles. Slow, thorough strokes along the bottom and sides for 2–3 minutes are better than fast mixing.

Frequently Asked Questions

What does a 2:1 epoxy mix ratio mean?

A 2:1 ratio means 2 parts resin (Part A) to 1 part hardener (Part B) by volume. For every 2 fl oz of resin you add 1 fl oz of hardener. Total batch = 3 fl oz. Part A is 66.7% of the mix, Part B is 33.3%.

How do I calculate Part A and Part B for a 2:1 ratio?

For a 2:1 ratio: Part A = total × 2/3, Part B = total × 1/3.

Example: Need 30 fl oz total → Part A = 20 oz, Part B = 10 oz. Use the quick calculator on this page for instant answers.

Is epoxy mix ratio measured by volume or by weight?

It depends on your product. Most consumer epoxies specify by volume (use measuring cups). Some industrial/marine systems specify by weight (use a digital scale). Check your product's label or technical datasheet — it will say explicitly.

What happens if my epoxy mix ratio is slightly off?

Errors within 2–3% generally result in slightly reduced hardness or longer cure time but the epoxy will still cure. Errors of 10% or more typically produce permanently soft, sticky, or brittle epoxy. Always measure accurately — don't estimate.

Which is better — 1:1 or 2:1 epoxy?

Neither is universally superior — it depends on the product chemistry. 1:1 is easier to measure. 2:1 systems often have higher hardness, better heat resistance, and longer pot life. Use whichever your chosen resin specifies — you can't change the ratio to improve performance.