Epoxy Mix Ratio Calculator

What Is an Epoxy Mix Ratio?

Epoxy systems are made from two main components: a resin (Part A) and a hardener (Part B). For the epoxy to cure correctly and reach full strength, these components must be mixed in the exact ratio specified by the manufacturer, such as 1:1, 2:1, or 5:1 (resin:hardener by parts).

These ratios can be specified by weight (grams, ounces) or by volume (milliliters, fluid ounces). If the ratio is not followed closely, the cured epoxy may remain soft, become brittle, or fail prematurely. This calculator helps you convert a resin:hardener ratio and a total desired mixed amount into precise portions for each component, so you can measure confidently and work more efficiently.

How the Epoxy Mix Ratio Calculator Works

Many epoxy products express their mixing instructions as a ratio of resin to hardener, written as r:1. The calculator assumes the second number in the ratio is 1 and that you enter the first number, r (for example, enter 2 for a 2:1 mix or 5 for a 5:1 mix). The tool then divides your total desired mixed amount between resin and hardener using a simple proportional formula.

If you need a total mixed amount T (in grams or milliliters), and the resin:hardener ratio is r:1, then:

• Resin amount =
• Hardener amount =

In MathML form, the resin portion can be written as:

The hardener portion is simply the remaining part of the total:

These fractions always add up to your total mixed amount T, ensuring that no material is unaccounted for. The calculator applies these formulas instantly when you submit the form and displays the recommended amounts of resin and hardener.

How to Use This Epoxy Mix Ratio Calculator

1. Find the resin:hardener ratio on your product label or technical datasheet. For example, 1:1, 2:1, 3:1, or 5:1 by weight or by volume.
2. In the Resin:Hardener Ratio field, enter only the first number of the ratio (the resin part). For a 2:1 system, enter 2. For a 1:1 system, enter 1.
3. In the Total Mixed Amount field, enter how much fully mixed epoxy you want to prepare. Choose a value that matches the units you intend to work with (for example, 150 if you want 150 grams).
4. Use the Units dropdown to select whether your total is in grams (by weight) or milliliters (by volume).
5. Optionally, enter an Extra Allowance (%) to account for waste, drips, or material left in the mixing cup. If you enter 5, the calculator will add 5% to the total and base the component amounts on that slightly higher target.
6. Press the calculate button. The calculator will display the recommended resin and hardener amounts. Measure these with a scale (for grams) or with graduated cups/syringes (for milliliters).

Choosing Between Grams and Milliliters

Most professional epoxy systems recommend mixing by weight for best accuracy. This is because the density of resin and hardener often differs, so a 2:1 ratio by volume may not be the same as 2:1 by weight. When in doubt, carefully read your product documentation to see whether the ratio is by weight or by volume.

If your product specifies a ratio by weight, use a digital scale, choose grams in the calculator, and measure each component accordingly. If your product specifies a ratio by volume, choose milliliters in the calculator and measure using graduated containers with clear markings.

Worked Example

Imagine you are laminating fiberglass and your epoxy specifies a 2:1 mix ratio by weight. You decide you need a total of 150 grams of mixed epoxy, and you want to allow for a small amount of waste.

Step through the process:

1. Enter 2 in the ratio field (for 2:1).
2. Enter 150 in the total mixed amount field.
3. Select grams as the units.
4. Set the extra allowance to 0 if you want exactly 150 g total.

The calculator computes:

• Resin = (2 / (2 + 1)) × 150 = (2 / 3) × 150 = 100 grams
• Hardener = (1 / (2 + 1)) × 150 = (1 / 3) × 150 = 50 grams

If you decide to add a 5% allowance for waste, your effective total becomes:

• Adjusted total T_adj = 150 × 1.05 = 157.5 grams

Now the calculator will base the portions on 157.5 g:

• Resin ≈ (2 / 3) × 157.5 ≈ 105.0 grams
• Hardener ≈ (1 / 3) × 157.5 ≈ 52.5 grams

This small buffer helps compensate for epoxy left on stir sticks, in the mixing cup, or absorbed into porous surfaces.

Typical Epoxy Ratios and Uses

Different epoxy formulations use different mix ratios depending on their chemistry and intended application. The table below shows some common resin:hardener ratios and where you might encounter them.

Always confirm the exact ratio and whether it is by weight or by volume for your specific product. Never assume two products with the same numerical ratio are interchangeable.

Mixing Tips for Reliable Results

Even with perfect ratios, epoxy performance depends heavily on how thoroughly and carefully you mix the components. Consider the following best practices:

• Measure accurately: Use a digital scale for grams and properly marked containers for milliliters. Avoid guessing or using unmarked cups.
• Mix in a clean container: Dust, oil, and leftover cured epoxy can all interfere with bonding and cure.
• Scrape sides and bottom: While stirring, regularly scrape the sides and bottom of the cup so all material is fully blended.
• Stir slowly and thoroughly: Mix for the time recommended by the manufacturer, usually several minutes. Stirring slowly helps reduce air bubbles.
• Observe pot life: Each epoxy has a limited working time before it begins to gel. Plan your work so that surfaces are ready before you mix.

Allowing for Waste and Application Loss

In real projects, not all of the epoxy you mix makes it onto the surface. Some is lost on mixing sticks, trapped in the corners of the container, or over-applied and then scraped off. Porous substrates such as raw wood or fabric can also absorb more epoxy than expected.

The Extra Allowance (%) input lets you account for this. A value of 3–10% is typical, depending on how carefully you work and how absorbent the materials are. For critical bonds or when coating rough or highly porous surfaces, leaning toward the higher side of that range can be helpful.

Managing Heat Build-Up (Exotherm)

The chemical reaction between resin and hardener releases heat, known as exotherm. Large batches in deep containers can become very hot, cure too quickly, or even damage nearby materials. To control this heat, mix only the amount you can apply within the stated pot life and consider dividing large batches into several smaller ones.

Pouring mixed epoxy into a wider, shallower tray reduces the depth of the liquid and allows heat to dissipate more easily. Avoid deep, narrow containers for large volumes, and never attempt to cool overheating epoxy with water while it is still liquid in the container. If a batch becomes very hot, place the container on a non-flammable surface and allow it to cure undisturbed.

Interpreting the Calculator Results

After you enter your ratio, total amount, units, and optional allowance, the calculator returns the recommended amounts of resin and hardener. Use these values as follows:

• If you chose grams: Tare your scale with an empty mixing cup, pour the resin until you reach the resin value in grams, then either add hardener directly to the same cup until the total weight reaches resin + hardener, or zero the scale again and pour the hardener separately.
• If you chose milliliters: Use a cup or syringe with clear volume markings and fill to the resin and hardener values indicated by the calculator. Take care to view the meniscus at eye level for accurate readings.

Once measured, combine the components and mix according to the manufacturer’s guidance, keeping in mind the pot life and correct application conditions.

Limitations, Assumptions, and Safe Use

This calculator is designed as a convenience tool and relies on a few important assumptions:

• Correct ratio input: It assumes you enter the correct resin part (the first number in the resin:hardener ratio) exactly as specified by your product. If your product uses a more complex ratio (for example, 100:45 by weight), you should convert this to an equivalent decimal ratio before use or follow the manufacturer’s measurement method directly.
• Manufacturer instructions take priority: Always follow the mixing and safety instructions on your epoxy’s label or technical datasheet, even if they differ from or refine the outputs of this calculator.
• Weight vs volume: The tool does not convert between weight and volume based on density. If your product specifies a ratio by weight and you choose milliliters, or vice versa, the numbers may not be accurate. Match the calculator units to the manufacturer’s specified basis.
• Rounding: For practicality, results may be rounded to the nearest sensible decimal place. For very small batches, rounding can introduce visible error; in those cases, consider making a slightly larger batch or using precision lab equipment.

For safe use of epoxy systems:

• Work in a well-ventilated area and avoid breathing fumes for prolonged periods.
• Wear suitable gloves, eye protection, and protective clothing to prevent skin and eye contact.
• Dispose of unused mixed epoxy and contaminated materials according to local regulations and the product’s safety data sheet.
• Keep resin, hardener, and mixed epoxy away from children, pets, sparks, and open flames.

The guidance in this explanation is based on common practices recommended by epoxy manufacturers and field use in woodworking, marine repair, composites, and crafts. It does not replace the specific instructions or safety information supplied with your product.