Epoxy flooring calculator

Epoxy coverage isn't a number on the kit — it's set by solids by volume and the dry-film thickness you build. Enter both and get gallons or litres by coat, with the coverage trap most garage-floor kits quietly rely on.

01 How the math works

Coverage comes from one identity, not from the label. A gallon of coating is a fixed volume. Spread it thinner and it covers more floor; spread it thicker and it covers less. The only wrinkle is solids by volume: the part of the can that stays on the floor after the water or solvent flashes off.

The 1604 is geometry, not a product spec: one US gallon is 231 in³, and spreading it at 1 mil (0.001 in) over 144 in² per square foot gives 231 ÷ 0.001 ÷ 144 = 1604.17 ft². The metric twin is an exact 1000 m²·µm per litre. A 100%-solids product keeps all of that; a 50%-solids product keeps half, because half the gallon leaves as the coating cures.

02 Worked example

Take a two-car garage floor: 24 ft × 24 ft (7.32 m × 7.32 m), which is 576 ft² (53.5 m²). Plan for two coats of a 100%-solids epoxy at a 10 mil dry film per coat.

At 100% solids and 10 mils, coverage is 1604 ÷ 10 = 160 ft²/gal (3.94 m²/L at 254 µm). Two coats over 576 ft² is 1,152 ft² of coating passes, so 1,152 ÷ 160 = 7.18 gal. Add a 10% waste factor and round up: 8 gallons (30 litres).

Now hold that against a water-based garage kit sold to cover "up to 500 ft²" from 1.875 gallons. That kit won't coat this 576 ft² floor even once at its best-case rate, and it builds roughly 3 dry mils where the plan called for 10. Same floor, same word on the label — a third of the coating on the slab.

03 When this calculator is wrong

The coverage figures a manufacturer prints are best-case numbers measured on smooth, low-porosity concrete. Most garage slabs aren't that. A rated figure like "up to 500 ft² per kit" is the ceiling, not the plan — the same 100%-solids product that works out to 160 ft²/gal from the identity is published at 115–170 ft²/gal precisely because porosity, surface profile, and waste pull real coverage below the theoretical number. Order at the low end of the range, not the headline. The exception is a floor that's already sealed or previously coated and still smooth; there the spec figure is close to honest.

• Coverage without a mil spec means nothing. A "500 ft²" kit and a "160 ft²/gal" product aren't the same product at different prices — they build different films. This calculator needs both solids% and target dry mils because the label's single coverage number hides the one that matters. Read the data sheet, not the front of the box.
• Wet film is not dry film. For any coating under 100% solids, the cured film is the wet film times the solids fraction. Roll a 50%-solids product at 10 wet mils and you keep 5 dry mils. If you're chasing a dry-film target, don't read the wet application rate as the finished thickness.
• The first coat on bare concrete drinks more. A primer coat or the first build coat on unsealed, open slab soaks into the surface, so first-coat coverage runs below the second. Budget the first coat thirstier than the identity suggests.
• It's coating only. The number here is epoxy to buy. It doesn't include concrete prep (etching or grinding), a separate primer, a topcoat, or broadcast media — flake or quartz is sold by the pound and ordered on its own.

04 What to do with the result

Order the rounded-up number, in whole kits or whole gallons, and buy it in one purchase. Epoxy is a two-part, pot-life product: once Part A and Part B are mixed, the clock is running, and you can't blend a fresh kit into a coat that's already going off. Running short mid-coat means a visible cold joint where the first batch skinned over before the next one landed. The cost of a spare gallon on the shelf is small next to that.

If your product lists a coverage figure on the data sheet rather than a solids percentage, you can enter that figure's implied dry film instead — solve the formula backward for the mils it assumes, and sanity-check it against the 8–12 mil range a 100%-solids garage system targets. If the implied film is 2–3 mils, you're looking at a thin water-based coating, not a built floor.

05 Common questions

How much epoxy do I need for a 2-car garage?

A 24 × 24 ft (576 ft² / 53.5 m²) two-car garage, two coats of 100%-solids epoxy at 10 mils, works out to 8 gallons (30 litres) with 10% waste. A thinner water-based system covers more area per gallon but builds far less film, so match the calculation to the product you're actually buying.

How many square feet does a gallon of epoxy cover?

It depends entirely on dry-film thickness and solids. A 100%-solids epoxy at 10 mils covers 160 ft²/gal; the same product published for real-world use is rated 115–170 ft²/gal. A thin water-based coating can read near 267 ft²/gal — but it's laying about 3 mils, not 10.

What is "solids by volume" and why does it matter?

It's the share of the can that stays on the floor after curing. A 100%-solids epoxy loses nothing, so wet film equals dry film. A 50%-solids product loses half its thickness as it cures, so you apply twice the wet film to hit the same dry film — and your coverage per gallon is halved.

How thick should a garage epoxy floor be?

A 100%-solids roller or squeegee system typically targets 8–12 mils of dry film per coat. Thin water-based kits land around 2–3 mils. More mils per coat means fewer square feet per gallon — the formula above makes the tradeoff explicit.

Do I count both coats in the coverage math?

Yes. Each coat is a full pass over the whole floor, so the coating passes are area × coats. The calculator multiplies by the coat count before dividing by coverage, then adds waste and rounds up.