Calculator · Interiors & furniture
Epoxy Resin Calculator for River Tables and Pours
Estimate epoxy for a river table or pour: mould volume less embedded wood, waste, layers by max pour depth, resin and hardener split, in litres and US gallons.
Epoxy pour calculator
Volume of mixed epoxy for a river table or cast pour, less the wood it surrounds, split into resin and hardener and into layers. Maximum depth per pour, mix ratio and density are product-specific: take them from the technical data sheet of the exact product you will use.
Result
Enter the pour size, the wood it surrounds and the product limits from its data sheet, then calculate.
How it works
This calculator estimates how much mixed epoxy a river table, inlay or cast pour needs. It starts with the volume of the mould or cavity, subtracts the wood that sits inside it, adds an allowance for waste and overfill, and then splits the result into resin and hardener by the mix ratio you enter and into separate pours by the maximum layer depth you enter.
Rivers rarely have parallel edges, so you can enter several widths measured along the river and the calculator uses their average. Results are given in litres, US gallons and US fluid ounces regardless of the unit system you choose.
No product data is built in. Maximum depth per pour, mix ratio and density differ between deep-pour casting resins and thin coating epoxies, and between brands. Read them from the technical data sheet of the exact product you will use.
- Mould volume = length × width × depth (average of measured widths in river mode).
- Displaced volume = slab length × slab width × slab thickness inside the pour × number of slabs, or mould volume × wood %.
- Net epoxy = mould volume − displaced volume.
- Epoxy to buy = net epoxy × (1 + waste % / 100).
- Litres = mm³ / 1,000,000; US gallons = litres / 3.785411784; fl oz = gallons × 128.
- Resin = total × resin parts / (resin parts + hardener parts); hardener = total × hardener parts / (resin parts + hardener parts).
- Layers = ceiling(total depth / maximum depth per pour); depth per layer = total depth / layers.
- Weight = litres × density (kg/L = g/mL); lb/gal density is converted with 1 lb = 0.45359237 kg.
Worked example
A 1200 × 500 mm mould filled 50 mm deep holds 30 L. Two slabs, each 1200 × 175 mm and fully submerged to 50 mm, displace 21 L, so the river needs 9 L of epoxy — less than a third of the mould volume.
Adding 10% for waste and overfill gives 9.9 L, or 2.62 US gal (335 fl oz). At an illustrative 2:1 volume ratio that is 6.6 L of resin and 3.3 L of hardener.
If the data sheet allowed 25 mm per pour, the 50 mm depth would be cast in 2 layers of 25 mm, about 4.95 L each. With an entered mixed density of 1.1 g/mL, the cured epoxy would weigh about 10.89 kg (24 lb). These three product values are examples only.
Common mistakes
- Calculating the whole mould volume and forgetting the slabs, which can overstate the epoxy several times over.
- Using a coating epoxy's thin-film limits for a deep pour, or a deep-pour resin's limits for a different product.
- Mixing by weight using a ratio published by volume (or the reverse).
- Pouring the full depth at once when the data sheet requires several layers.
- Leaving no allowance for seal coats, mixing-cup residue, leaks and overfill.
Scope and limits
- Volumes assume vertical sides: the river is the same width at the top and bottom of the pour.
- Slab displacement uses rectangular blocks; live edges, voids and bark inclusions are approximated by the average slab width.
- No resin product data is built in; pour depth limits, mix ratio, density, cure time and temperature limits must come from the manufacturer.
- This is a volume estimate, not safety guidance. Follow the manufacturer's safety data sheet for ventilation, skin protection and exotherm risk.
Common questions
How much epoxy do I need for a river table?
Multiply the river length by its average width and the pour depth, then add a waste allowance. If you measure the whole mould instead, subtract the volume of the slabs inside it.
How many litres are in a US gallon?
One US gallon is 231 cubic inches, which is exactly 3.785411784 litres, and contains 128 US fluid ounces.
How deep can I pour epoxy in one layer?
It depends entirely on the product. Deep-pour casting resins and coating epoxies have very different limits. Use the maximum depth on your product's technical data sheet; this calculator does not supply a default.
Why does the wood need a seal coat?
Air in the wood can escape into the pour and form bubbles. Manufacturers' river-table instructions call for thin seal coats on the wood before the main pour.
Is the mix ratio by volume or by weight?
Data sheets may give either or both. This calculator splits the mix by volume, so enter the volume ratio. Resin and hardener usually have different densities, so the weight ratio is not the same number.
Can it estimate the weight of the epoxy?
Yes, if you enter the mixed density from the product data sheet in g/mL or lb per US gallon. It does not guess a density.
Sources
- NIST Guide to the SI, Appendix B.8: Factors for units listed alphabeticallyNational Institute of Standards and TechnologyConversion factors for the US gallon (3.785 412 L), US fluid ounce (29.573 53 mL), inch and pound.
- The Basics of Uncontrolled CureWEST SYSTEM (Gougeon Brothers)Explains that a larger or thicker mass of mixed epoxy generates more heat and advises filling large cavities in multiple layers.
- TotalBoat Epoxy River Table Kit InstructionsTotalBoatOne manufacturer's river-table instructions: seal coats to stop air in the wood off-gassing, a 1:1 volume ratio and a maximum of 1/2 in per layer for that kit, and volume as length × width × depth (231 in³ per gallon).