Volume is area times thickness — everything else is a unit swap
Keep the units consistent. Work the area and thickness in inches to get cubic inches, then convert: one cubic inch is 0.554 fl oz, and there are 128 fl oz to a US gallon. A flood coat is usually 1/8 inch (0.125 in); a seal coat is far thinner.
Coverage of one gallon by coat thickness
| Coat thickness | Coverage per gallon | Typical use |
|---|---|---|
| 1 mil (0.001 in) | ~1,600 sq ft | Thin sealer |
| 1/16 in (62.5 mil) | ~25 sq ft | Light coat / doming |
| 1/8 in (125 mil) | ~12–13 sq ft | Standard flood coat |
| 1/4 in (250 mil) | ~6 sq ft | Deep pour / casting |
Deep casting pours usually cap the layer depth per pour (often 1/2 to 2 inches depending on the product) to keep the heat down. Splitting a thick pour into layers is normal.
Get the mix ratio right, and buy extra
- Ratio is not interchangeable. A weight ratio of 100:47 (resin:hardener) is common; by volume the same system is often near 2:1. Use the one printed on your kit and stick to it.
- Off-ratio does not cure right. Too much resin stays tacky and soft; too much hardener goes brittle and can leave a greasy residue. There is no fixing it after cure.
- Add a buffer. Order 10–15% over the calculated volume for cup residue, tool loss and low spots.
Common questions
How much epoxy do I need for a table top?
Multiply the area by the coat thickness. For a flood coat, area in square inches times 0.125 inch (an eighth) gives cubic inches; divide by 1.805 for fluid ounces. A 24 by 48 inch top at an eighth of an inch needs about 96 fl oz, roughly three quarts.
Should I mix epoxy by weight or by volume?
Follow whatever the label states, and never swap the two. Resin and hardener have different densities, so a 2 to 1 ratio by volume is not 2 to 1 by weight. If the label gives a weight ratio like 100:47, use a scale.
Why add extra epoxy to the calculated amount?
Because some stays in the mixing cup, clings to brushes and rollers, and fills low spots you did not measure. A 10 to 15 percent buffer covers this. It is far cheaper than running short mid-pour and getting a visible cure line.
