Quick answer: measure the void, then fluid ounces = cubic inches ÷ 1.805. For a flood coat there is a simpler rule: one gallon covers about 12 ft² at 1/8 inch. Order 10% extra — wood absorbs resin and some always stays in the mixing cup.
Before you pour: epoxy cures by an exothermic reaction, and pouring deeper than your product allows can generate enough heat to crack, yellow or smoke the piece. Check the maximum pour depth on your specific resin — it is the number that matters most on this page.
Pour depth limits by resin type
| Resin type | Max pour depth | Typical cure | Use for |
|---|---|---|---|
| Tabletop / coating | 1/8 in per layer | 12–24 h between coats | Flood coats, bar tops, art |
| General purpose | 1/4 in per layer | 24 h | Small castings, seal coats |
| Deep pour / casting | 1–2 in per layer | 36–72 h | River tables, moulds |
| Ultra deep pour | 2–4 in per layer | 3–7 days | Thick single-pour castings |
The trade-off is straightforward: deeper pours need slower resins so the reaction heat has time to dissipate. Rushing a river table with tabletop epoxy is the classic beginner mistake — it goes off hot, cracks, and the whole slab is wasted.
Flood coat coverage
| Thickness | ft² per gallon | fl oz per ft² |
|---|---|---|
| 1/32 in (seal coat) | 48 | 2.7 |
| 1/16 in | 24 | 5.3 |
| 1/8 in (standard flood) | 12 | 10.7 |
| 1/4 in | 6 | 21.3 |
| 1/2 in | 3 | 42.7 |
Worked example — a 3 × 6 ft table at a 1/8 inch flood coat: 18 ft² ÷ 12 = 1.5 gallons. Add 10–15% for edge drips, which on a flood coat can be surprisingly generous, and order two gallons.
River tables: measuring an irregular void
River channels are rarely straight, which makes measuring the void the real work. The practical approach:
- Measure the channel width at five or six points along its length and average them.
- Use the full length of the channel, and its deepest point as the depth (the slab edges taper, but resin fills to a level surface).
- Multiply the three, then divide cubic inches by 1.805 for fluid ounces.
- Add 10% for absorption into the wood and residue in the mixing cup.
Example: a channel averaging 6 inches wide, 60 inches long, 1.75 inches deep is 630 in³ ≈ 349 fl oz ≈ 2.7 gallons. With a 2-inch deep-pour resin that is one pour; with tabletop epoxy it would be fourteen layers and several weeks, which is why deep-pour resin exists.
A tip that saves money: seal the wood with a thin coat of epoxy before the main pour. Bare end grain drinks resin, and air escaping from the wood into a curing deep pour causes bubbles that are impossible to remove later.
Common mistakes & pro tips
- Adjusting the mix ratio. Extra hardener does not cure faster or harder — it leaves a soft, tacky finish that never fully sets. Measure precisely.
- Pouring deeper than the resin allows. The exotherm cracks, yellows and occasionally smokes. Layer, or buy deep-pour.
- Forgetting the mould leaks. Resin finds every gap. Tape and seal the form before you mix.
- Pouring cold. Most epoxies want 70–75 °F. Cold resin traps bubbles and cures slowly or incompletely.
- Pro tip — mix in two vessels. Combine, stir thoroughly, then scrape into a second clean cup and stir again. Unmixed resin clinging to the first cup's walls is the most common cause of soft patches.
- Pro tip — order generously. Running out mid-pour on a river table leaves a visible cure line that cannot be sanded out. Extra resin keeps; a ruined slab does not.
Frequently asked questions
How much epoxy do I need for a river table?
Measure the void between the slabs — average width × length × depth — and convert to fluid ounces by dividing cubic inches by 1.805. A river channel 6 inches wide, 60 inches long and 1.75 inches deep is 630 in³, about 349 fluid ounces or 2.7 gallons. Add 10 percent for waste and the wood soaking some up.
How do I convert cubic inches to fluid ounces of resin?
Divide cubic inches by 1.805, since one US fluid ounce is 1.805 cubic inches. For a tabletop coating, there is a well-known shortcut: one gallon of epoxy covers about 12 square feet at 1/8 inch thick.
What is the mix ratio for epoxy resin?
It varies by product — 1:1, 2:1 and 3:1 by volume are all common, and some systems mix by weight instead. The ratio is not adjustable: epoxy cures by chemical reaction, so adding extra hardener does not speed it up, it produces a soft or permanently tacky finish. Always follow the specific product's instructions.
How deep can I pour epoxy in one go?
Depends on the formulation. Standard tabletop epoxy is limited to about 1/8 to 1/4 inch per layer, while deep-pour casting resins allow 1 to 2 inches or more. Exceeding the limit causes overheating — the exotherm can crack the piece, yellow it, or in extreme cases smoke. Deep-pour resin is slower precisely so heat can escape.
How much epoxy do I need to coat a tabletop?
At the usual 1/8 inch flood coat, roughly one gallon per 12 square feet. A 3 × 6 ft table is 18 square feet, so about 1.5 gallons. Add extra for the drips down the edges, which are substantial on a flood coat.