Formula
Volume from the shape, waste on top, then the US gallon identity for fluid ounces.
rectangle = length × width × depth
cylinder = π × (diameter ÷ 2)² × depth
channel = length × average width × depth
fl oz = in³ × 128 ÷ 231
ml = in³ × 16.387064
Waste is applied before the parts are split. Part A is ratio A ÷ (A + B) of the mixed volume. Density turns millilitres into grams and does not change the volume.
Worked examples
12 × 12 × ⅛ inch, no waste, 1:1. Volume = 18 in³. That is 18 × 128/231 = 9.97 fl oz, about 295 ml. Each part is half.
Same pour with 10% waste. Mix 10.97 fl oz. At 1.1 g/ml that is about 357 grams of mixed resin.
Reference
No waste, 1:1, density 1.1 g/ml. The river is a rectangular channel, which is the right model when you have an average width.
| Pour | in³ | fl oz | ml |
|---|---|---|---|
| 12×12×⅛ in board | 18 | 9.97 | 295 |
| 3 in tumbler, 4 in deep | 28.27 | 15.67 | 463.3 |
| 24 in river, 1.5×0.5 in | 18 | 9.97 | 295 |
Questions
How much epoxy do I mix for a pour?
Compute the volume of the cavity, add a waste percentage, and convert cubic inches to US fluid ounces with 128/231. A 12 by 12 by ⅛ inch flood is 18 cubic inches, about 10 fluid ounces before waste. Split that mixed volume by the parts ratio on the bottle.
Is a resin calculator the same as an epoxy resin calculator?
For a volume pour, yes. The geometry does not care about the brand. The mix ratio does. A 1:1 resin splits in half. A 2:1 resin is two parts of A and one part of B, by volume, of the same mixed total.
Why is the fluid-ounce factor 128/231?
One US gallon is defined as 231 cubic inches and as 128 US fluid ounces. So one cubic inch is 128/231 fluid ounces, about 0.554. Millilitres use the international inch: 1 in³ = 16.387064 ml.
What density should I use?
About 1.1 grams per millilitre is a fair planning figure for mixed epoxy. The bottle or the SDS wins if it prints one. The volume in fluid ounces does not depend on density. Only the gram weight does.
Sources
- US gallon: 231 cubic inches = 128 US fluid ounces. NIST Handbook 44, Appendix C.
- International inch: 1 in = 2.54 cm exactly, so 1 in³ = 16.387064 cm³ = 16.387064 ml.