How the calculation works
US gallons = cubic inches ÷ 231 · litres = cubic centimetres ÷ 1,000
Epoxy to buy = volume × (1 + waste %)
A US gallon is exactly 231 cubic inches (3.785 litres) — the definition used by NIST. The calculator adds 10% by default for epoxy left in mixing cups, slow leaks from the form and resin soaked up by the wood; EcoPoxy’s own volume guide adds 5%. Live-edge slabs with bark pockets, cracks or deep voids may need more.
Maximum pour depth by product
Deep-pour epoxies cure slowly so the heat of the reaction can escape. Pour deeper than the label allows and the resin can overheat, crack, bubble or yellow. When your project is deeper than one pour, the calculator splits it into layers.
| Epoxy | Max depth per pour | Mix ratio | Notes |
|---|---|---|---|
| TotalBoat ThickSet Fathom | 2 in (5.1 cm) | 2:1 by volume | 2 in for slabs, 3 in for castings |
| TotalBoat ThickSet Cast + Coat | 0.5 in (1.3 cm) | 1:1 by volume | ½ in for slabs, 2 in for small castings |
| EcoPoxy FlowCast | 1.5 in (3.8 cm) | 2:1 by volume | 0.5–1.5 in applies to pours up to 30 L; 2.3:1 by weight |
| MAS Deep Pour | 0.5 in (1.3 cm) | 3:1 by volume | ½ in for a full 1.3 gal kit, 1 in for a half kit; larger slabs should be poured thinner |
| Stone Coat Woodshop Ultra Deep | 3 in (7.6 cm) | 2:1 by volume | 3 in per layer in moulds; mix no more than 5 gal at a time |
Depths are for typical room temperatures and the conditions on each manufacturer’s page — some apply only up to a certain volume per pour (EcoPoxy FlowCast: 30 L), some are for moulds rather than slabs, and Stone Coat says not to mix more than 5 gallons at a time. Larger volumes, warm rooms and thick moulds reduce the safe depth; the calculator warns when a pour goes past a stated volume. Always check the current label for your batch.
River table epoxy chart
Epoxy for common river channels, including 10% extra:
| Channel (L × W × D) | US gallons | Litres | Weight |
|---|---|---|---|
| 24 × 4 × 1 in | 0.46 | 1.7 | 1.9 kg / 4.2 lb |
| 36 × 4 × 1.5 in | 1.03 | 3.9 | 4.3 kg / 9.4 lb |
| 36 × 6 × 1.5 in | 1.54 | 5.8 | 6.4 kg / 14.2 lb |
| 48 × 4 × 1.5 in | 1.37 | 5.2 | 5.7 kg / 12.6 lb |
| 48 × 6 × 1.5 in | 2.06 | 7.8 | 8.6 kg / 18.9 lb |
| 48 × 6 × 2 in | 2.74 | 10.4 | 11.4 kg / 25.2 lb |
| 60 × 6 × 2 in | 3.43 | 13.0 | 14.3 kg / 31.5 lb |
| 60 × 8 × 2 in | 4.57 | 17.3 | 19.0 kg / 42.0 lb |
| 72 × 6 × 2 in | 4.11 | 15.6 | 17.1 kg / 37.8 lb |
| 72 × 8 × 2 in | 5.49 | 20.8 | 22.8 kg / 50.4 lb |
| 72 × 10 × 2 in | 6.86 | 26.0 | 28.6 kg / 62.9 lb |
| 84 × 8 × 2 in | 6.40 | 24.2 | 26.6 kg / 58.8 lb |
| 84 × 12 × 2 in | 9.60 | 36.3 | 40.0 kg / 88.1 lb |
| 96 × 8 × 2 in | 7.31 | 27.7 | 30.5 kg / 67.1 lb |
| 96 × 12 × 2 in | 10.97 | 41.5 | 45.7 kg / 100.7 lb |
| 96 × 12 × 2.5 in | 13.71 | 51.9 | 57.1 kg / 125.9 lb |
| 48 × 24 × 1 in | 5.49 | 20.8 | 22.8 kg / 50.4 lb |
| 72 × 36 × 1 in | 12.34 | 46.7 | 51.4 kg / 113.3 lb |
Measuring a river table
- Seal the slabs and the form. Seal porous wood with a thin coat of epoxy first and tape or seal the form; leaks are the commonest reason to run short.
- Measure the river in sections. Measure the width every 6–12 inches along the channel and use the average. Wavy live edges make the ends very different from the middle.
- Use the full depth to be filled — usually the slab thickness, plus a little to allow for flattening the top.
- Mix only what one pour needs. Kits are sized by volume; buy enough for all layers, but mix each layer separately.
Mixing by volume or by weight
Most deep-pour kits give a ratio by volume. If you mix on a scale, use the manufacturer’s ratio by weight, which is different because the resin and hardener have different densities — EcoPoxy FlowCast, for example, is 2:1 by volume but 2.3:1 by weight. Mixed epoxy weighs about 1.1–1.2 kg per litre (WEST SYSTEM 105 cures at a specific gravity of 1.15–1.18, data sheet).
Safety. Work in a ventilated space, wear nitrile gloves and eye protection, and follow your product’s safety data sheet. Large masses of mixed epoxy left in a bucket can overheat and smoke — pour promptly.
Last reviewed: 2026-10-04 · Disclaimer