Epoxy is measured by volume: length × width × depth, in cubic inches, divided by 231 gives US gallons. A 6 × 3 ft river table poured 1½ in deep, with the river taking a quarter of the top, holds 972 cu in of epoxy. Add 10% for what stays in the cup and on the stick and you need 4.63 gallons (17.5 L, 592 fl oz) of mixed resin and hardener.
How the epoxy calculator works
Every project comes down to a volume, and the volume to gallons:
gallons = volume in cu in × (1 + waste %) ÷ 231
liters = gallons × 3.785; fluid ounces = gallons × 128
- River table: table length × width × pour depth × the share of the top that is river.
- Bar top or countertop: (top area + perimeter × edge height) × coat thickness × coats. A flood coat self-levels to about ⅛ in, which is 125 mils.
- Garage floor: floor area × film thickness per coat × coats. One gallon spread 1 mil thick covers 1,604 sq ft (231 cu in ÷ 0.001 in ÷ 144), so at 10 mils a gallon covers 160.4 sq ft per coat.
- Casting or mold: length × width × depth for a box, π ÷ 4 × diameter² × depth for a round mold, times the number of molds.
The mixed volume is then split by the kit's mix ratio (1 : 1 or 2 : 1 by volume) into resin and hardener, and the depth is divided by the thickest pour your product allows.
Worked example: river table, bar top, garage floor, casting
- River table, 6 ft × 3 ft × 1½ in, 25% river: 72 × 36 × 1.5 × 0.25 = 972 cu in. With 10%: 1,069 cu in ÷ 231 = 4.63 gal, 17.5 L, 592 fl oz. EcoPoxy FlowCast mixes 2 : 1, so 3.09 gal resin and 1.54 gal hardener, in one pour (up to 1½ in). In 12 L kits that is 2 kits.
- Bar top, 8 × 2 ft, ⅛ in flood coat, 1½ in edges: top 2,304 sq in plus edges 240 in × 1.5 in = 360 sq in, × 0.125 in = 333 cu in. With 10%: 1.59 gal, 6.0 L, 203 fl oz.
- Garage floor, 20 × 20 ft, two coats at 10 mils: 400 × 2 ÷ 160.4 = 4.99 gal, with 10% 5.49 gal (20.8 L). Sold as kits, one Epoxy-Coat Better full kit covers 500 sq ft with base and clear coat.
- Casting, one 10 × 4 × 2 in mold: 80 cu in, with 10% 88 cu in = 0.38 gal, 48.8 fl oz, 1.44 L.
Deep pour epoxy: how thick can one layer be?
Deep pour epoxy cures slowly so the heat of the reaction can escape; pour it thicker than the maker allows and it can crack, yellow or ripple. The calculator splits your depth into pours using these limits, taken from each manufacturer:
| Product | Maximum per pour | Mix ratio | Notes from the maker |
|---|---|---|---|
| EcoPoxy FlowCast | 1½ in | 2 : 1 | 65 to 75 °F, a fan on the pour, under 20 L per pour, about 24 h between layers |
| MAS Deep Pour X | 2 to 3 in | 2 : 1 | "should be poured 2-3" thick per pour" |
| TotalBoat ThickSet | ½ in | 1 : 1 | 2 in only for small castings under 10 oz |
| Tabletop / bar top epoxy | about ⅛ in | check the kit | a flood coat; build thicker tops in coats |
The river table above is one pour of FlowCast, one pour of Deep Pour X, or three ½ in pours of ThickSet. Mix only one pour's worth at a time: a whole batch in one bucket gets hot fast.
How much epoxy for a countertop or bar top
TotalBoat puts most tabletop epoxies at about 12 sq ft per mixed gallon at ⅛ in. The pure geometry is 12.8 sq ft (144 sq in × 0.125 in = 18 cu in per sq ft, and 231 ÷ 18 = 12.8), so the rest is loss. Coating the edges adds perimeter × edge height; masking them off saves that. Two coats double it. You can enter the thickness in inches or in mils.
Epoxy for a garage floor
Floor coatings are specified in mils (thousandths of an inch) per coat. Epoxy-Coat describes its single-coat kit at about 10 mils and its base plus clear coat at about 20 mils, which is why the default is two coats of 10 mils. For a 100% solids epoxy the wet film is also the dry film; a water-based product loses its water as it dries, so follow the coverage on its label. The Dampney Company's coating guide suggests deducting 10% from theoretical coverage for losses, which matches the default waste.
What to do next
- Price the whole floor with grinding, crack repair and labor in the epoxy flooring cost calculator.
- Buying the slabs for a river table? Price them in the board foot calculator.
- An epoxy countertop over an old top? Size the top and seams with the countertop calculator.
- Pouring into a bigger form? The cubic feet calculator gives its volume in cubic feet.
More floor and finish tools are on the floors, tile and trim page.