Epoxy Resin Calculator
| Project | Mold (L x W x D in) | Mixed epoxy |
|---|---|---|
| Coaster set pour | 4 x 4 x 1/8 | 0.01 gal (1.1 fl oz) |
| Cutting board coat | 18 x 12 x 1/8 | 0.12 gal (15 fl oz) |
| Serving tray | 24 x 16 x 1/8 | 0.21 gal (26.6 fl oz) |
| Bar top, one stage | 120 x 25 x 3/16 | 2.44 gal |
| River table, 1/4 in | 96 x 36 x 1/4 | 3.74 gal |
Epoxy is bought in kit gallons and mixed in exact halves, but projects are measured in inches - a river table is 96 x 36 inches, a coat is an eighth of an inch deep, and the gap between those units is where orders go wrong. This calculator bridges them: length x width x depth gives cubic inches, 231 of those make a US gallon, and the output splits the total into equal resin and hardener parts for 1:1 systems.
Bottom line: a 8-foot by 3-foot river table at a 1/4-inch deep pour is 96 x 36 x 0.25 = 864 cubic inches - 3.74 gallons, or 1.87 gallons each of resin and hardener - and with the 10% that stays stuck to the cup and stir stick, order a 4-gallon kit, not a 3.75-gallon plan.
The honest part: depth is the whole ballgame. Thin seal coats (1/16 inch) go on one pass, but pours past 1/8 inch in a standard tabletop resin generate heat faster than they shed it - the exotherm that yellows, cracks or boils a deep pour. Anything deeper than 1/8 inch in one pass needs a slow-cure deep-pour resin and usually multiple staged pours, which is why river tables are poured in layers, not all at once.
How to use
- Measure the mold's inside length and width in inches - the pour area, not the slab size.
- Pick a pour depth: 1/16 for a seal coat, 1/8 for a standard coat, 1/4 for bar tops, or enter your own for deep pours.
- Read gallons and the A/B split, add 10% for mixing loss, and check the table for how many staged pours your depth implies.
Frequently asked questions
How much epoxy do I need for a river table?
An 8-foot by 3-foot river table at 1/4 inch deep takes 96 x 36 x 0.25 = 864 cubic inches = 3.74 US gallons of mixed epoxy - about 1.9 gallons of resin plus 1.9 of hardener on a 1:1 system. Add 10% mixing loss and buy a 4-gallon kit. Most builds split that into two or three staged pours of 1/8 inch each with a deep-pour resin; a standard tabletop resin should never take the whole volume in one pass.
Why divide by 231 for gallons?
A US gallon is legally 231 cubic inches - the old wine gallon Congress standardized in 1832, before the metric liter. Epoxy coverage math lives in cubic inches (inches x inches x inches), kits live in gallons, and 231 is the exchange rate between them: 27 cubic inches (a cutting board coat) is 0.117 gallons, about 15 fluid ounces. In metric, 61.02 cubic inches make a liter, so the same pour is 0.44 liters.
What is the 1:1 rule and why does hardener not change coverage?
Most tabletop epoxies mix resin and hardener in equal volumes - the kit's two jugs are matched so a '1-gallon kit' is half resin, half hardener, yielding one mixed gallon. Some systems run 2:1 or 4:1 by volume (or by weight - never confuse the two); those kits split differently but the mixed total still equals your pour volume. The coverage math never changes: total mixed volume is what fills the mold, and the split just divides it between jugs.
Why did my deep pour crack or bubble?
Exotherm: epoxy cures by an exothermic reaction, and a thick mass traps its own heat - past roughly 1/8 inch, standard resin can exceed 200 F in the core, boiling off bubbles, yellowing, and pulling away from the mold in cracks. The fixes are physics, not brand-hopping: pour in 1/8-inch stages, use a slow-cure deep-pour resin rated for 2-plus inches per pass, mix smaller batches per stage, and let each stage cool fully before the next. Thin seal coats first also release the air that bubbles up from raw wood.