How do I calculate how much epoxy resin I need?

Measure your mold's internal dimensions (length × width × depth in mm), calculate the volume in ml, then multiply by the resin's mixed density to get total grams. Add 10% for waste in mixing cups.

What is the difference between weight ratio and volume ratio for epoxy?

Some resins specify their A:B ratio by weight (measure on a scale) while others specify by volume (measure in graduated cups). Using the wrong method will result in improper curing. Always check your resin's technical data sheet.

Why does my epoxy stay sticky after curing?

Sticky or soft epoxy is almost always caused by incorrect mixing ratios. Even small deviations (2-3%) can prevent full cure. Use a digital scale accurate to 0.1g for precise measurement.

Epoxy Resin Ratio Calculator - Free Mixing Calculator

How It Works

Epoxy resin cures through a chemical reaction between two components: resin (Part A) and hardener (Part B). The ratio between these parts is critical — even a 5% deviation can prevent full cure, leaving a sticky or soft surface.

Different brands specify their ratios either by weight or by volume. Weight-ratio resins (like West System 5:1) are measured on a scale. Volume-ratio resins (like ArtResin 1:1) are measured in graduated cups. Using the wrong method is the most common beginner mistake.

This calculator handles both methods automatically. Select your resin brand or enter a custom ratio, and it converts between volume and weight using each component's specific density.

The Formulas

From mold volume:

Calculate mold volume: Length × Width × Height ÷ 1000 (for mm to ml)
Add waste margin (typically 10% for cup/stick residue)
For weight-ratio resins: Total weight = Volume × Mixed density, then split by ratio
For volume-ratio resins: Split volume by ratio, then multiply each by its specific density

From known Part A:

For weight ratio: Part B = Part A × (Ratio B ÷ Ratio A)
For volume ratio: Convert Part A to volume using density A, apply ratio, convert back using density B

How to Use This Calculator

Choose your resin from the preset list or enter custom values
Select your mode:
- Mold Volume — enter mold dimensions or direct volume
- From Part A — enter the weight of Part A you've already measured
Set waste margin (Mold mode only) — 10% is standard for small projects
Read results — Part A and Part B weights displayed in grams
Export PDF for workshop reference

Tips & Safety Notes

Always measure by weight when possible, even for "volume ratio" resins — it's more accurate
Temperature matters: Cold resin is thicker and harder to mix. Warm both parts to 20-25°C before mixing
Mix thoroughly for at least 3 minutes, scraping sides and bottom of the cup
Large pours generate heat — pours over 500ml should be done in layers to prevent overheating (exothermic reaction)
Wear nitrile gloves (not latex) and safety glasses. Work in ventilated spaces
Shelf life: Most resins last 6-12 months. Yellowed or cloudy resin may not cure properly

Related Tools

Candle Wax & Fragrance Calculator — similar volume-to-weight calculations for wax crafting
Box Template Creator — design molds and containers for your resin projects

FAQ

Can I mix different brands of resin and hardener?

Never mix Part A from one brand with Part B from another. Each system is chemically formulated as a pair. Cross-mixing will likely result in incomplete cure.

What if I don't know my resin's density?

Use 1.10 g/ml as a safe estimate for most clear casting resins. For precise work, weigh a known volume (fill a 100ml graduated cylinder and weigh it).

How much extra should I mix for waste?

10% covers most small-to-medium projects. For very small molds under 50ml, mix 15-20% extra since proportionally more resin sticks to the cup and mixing stick.

Last reviewed: June 2026