# How much epoxy do I need?

Computes the volume of epoxy resin to coat or pour a rectangular or round surface to a thickness, with extra for waste, in gallons, fluid ounces and litres, and how much resin and hardener to mix.

- Page: https://www.acalculator.org/construction/epoxy-calculator
- JSON spec: https://www.acalculator.org/construction/epoxy-calculator.json
- Version: e3b18783a7dd

## Default answer

Example with the default inputs (Shape Rectangle, Length 4 ft, Width 2 ft, Thickness 0.125 in, Extra for waste 10%, Resin parts 1, Hardener parts 1): Mix 0.686 gal (2.596 L) of epoxy: 43.9 fl oz of resin and 43.9 fl oz of hardener.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| shape | Shape | Whether the surface is a rectangle or a circle. |
| l | Length | The length of the surface. |
| w | Width | The width of the surface. |
| d | Diameter | The diameter of a round surface. |
| t | Thickness | How thick the epoxy layer is: the coat or the pour depth. |
| extra | Extra for waste | Epoxy to add on top of the layer volume, in percent, for drips over the edges and resin left in the cup. |
| a | Resin parts | The resin part of the mix ratio by volume: 1 for a 1:1 epoxy, 2 for 2:1. |
| b | Hardener parts | The hardener part of the mix ratio by volume, usually 1. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| gallons | US gallons | The epoxy to mix, in US gallons (231 in³ each). |
| fluidOunces | Fluid ounces | The epoxy to mix, in US fluid ounces (128 to the gallon). |
| liters | Litres | The epoxy to mix, in litres. |
| resinOunces | Resin, fluid ounces | The resin part of the mix, in US fluid ounces. |
| hardenerOunces | Hardener, fluid ounces | The hardener part of the mix, in US fluid ounces. |
| resinMl | Resin, millilitres | The resin part of the mix, in millilitres. |
| hardenerMl | Hardener, millilitres | The hardener part of the mix, in millilitres. |

## Method

Volume = length × width (or π × diameter² ÷ 4) × thickness × (1 + extra ÷ 100); resin = volume × a ÷ (a + b); hardener = volume × b ÷ (a + b), for an a:b mix by volume.

## Assumptions

- The epoxy spreads to an even thickness over the whole surface; a rough or porous surface soaks up more.
- Extra for waste is 10% by default, for drips over the edges and resin left in the mixing cup.
- The mix ratio is by volume. For an epoxy mixed by weight, use the maker’s weights instead.

## Worked examples

1. shape = rect, l = 1.2192, w = 0.6096, t = 0.003175, extra = 10%, a = 1, b = 1 gives gallons = 0.685714, fluidOunces = 87.771429, liters = 2.595711, resinOunces = 43.885714, resinMl = 1,297.855469. Source: NIST Handbook 44, Appendix C (1 US gallon = 231 in³ = 128 fl oz = 3.785411784 L).
2. shape = rect, l = 1, w = 0.5, t = 0.002, extra = 0%, a = 2, b = 1 gives liters = 1, resinMl = 666.666667, hardenerMl = 333.333333, gallons = 0.264172. Source: NIST Handbook 44, Appendix C (1 L = 0.001 m³).
3. shape = circle, d = 0.9144, t = 0.00635, extra = 0%, a = 1, b = 1 gives gallons = 1.101597. Source: NIST Handbook 44, Appendix C (1 gal = 231 in³).

## FAQ

### How do I calculate how much epoxy I need?

Multiply the length by the width by the thickness to get the volume, in one unit. A 48 × 24 in table top with a 1/8 in coat needs 48 × 24 × 0.125 = 144 cubic inches. There are 231 cubic inches in a US gallon, so that is 0.62 gallon, or 79.8 fl oz. Add about 10% for drips and the resin left in the cup.

### How much epoxy do I need for a river table?

Measure the river (the gap between the slabs) as a rectangle, or several rectangles, and use the full pour depth as the thickness. A river 72 in long, 6 in wide and 1.5 in deep holds 72 × 6 × 1.5 = 648 in³, which is 2.81 gallons before waste. Deep pours need an epoxy made for thick layers.

### How thick should an epoxy coat be?

Many table-top epoxies self-level to about 1/8 in (3 mm) per coat, so 1/8 in is the default here. Deep-pour casting resins can be poured much thicker in one go. Check the maximum pour depth on your epoxy’s label.

### What does a 1:1 or 2:1 mix ratio mean?

It is how many parts of resin go with how many parts of hardener, by volume. For 1:1, half the mix is resin and half is hardener. For 2:1, two-thirds is resin and one-third is hardener: 1 litre of 2:1 epoxy is 666.7 mL of resin and 333.3 mL of hardener.

### How many fluid ounces are in a gallon of epoxy?

A US gallon is 128 US fluid ounces, 231 cubic inches, or exactly 3.785411784 litres. A “1 gallon kit” of 1:1 epoxy usually means half a gallon of resin and half a gallon of hardener.

### Why add extra for waste?

Some epoxy runs over the edges, some stays in the mixing cup and on the spreader, and a porous surface soaks some up. The calculator adds 10% by default; set it to 0% for the layer volume alone.

## Sources

- NIST Handbook 44 (2024), Appendix C, General Tables of Units of Measurement: 1 US gallon = 231 in³ = 128 US fl oz = 3.785411784 L; 1 L = 1,000 mL = 0.001 m³. https://www.nist.gov/pml/owm/nist-handbook-44-current-edition
- OpenStax, Prealgebra 2e, §9.6 Solve Geometry Applications: Volume and Surface Area (volume of a rectangular solid and of a cylinder). https://openstax.org/books/prealgebra-2e/pages/9-6-solve-geometry-applications-volume-and-surface-area