How much epoxy do I need for my floor? Using the calculator
- 1Measure the floor, or enter the area directly, and the number of coats.
- 2Choose where the coverage comes from: the label of your product, or a 100 % solids epoxy at the dry thickness you want.
- 3Choose the kit size, and the spare for porous concrete and roller losses.
- 4Read how many kits to buy and how much epoxy each coat takes.
Epoxy coverage formula (1604 ÷ mils)
- 01Epoxy = floor area × coats ÷ coverage per coat × (1 + spare %)
- 02Kits = epoxy ÷ kit volume, rounded up
- 03100 % solids: coverage (ft²/gal) = 1604 ÷ dry thickness (mils)
- 04Any coating: coverage = 1604 × volume solids ÷ mils (= 1,000 × volume solids ÷ µm m²/L)
A US gallon is 231 cubic inches. Spread 1 mil (a thousandth of an inch) thick it covers 231 ÷ 0.001 = 231,000 in², which is 1604 ft². A 100 % solids epoxy stays as thick as you roll it, so at 10 mils one gallon covers 1604 ÷ 10 = 160 ft². In metric, a litre spread 1 µm thick covers 1,000 m², so at 250 µm a litre covers 4 m².
Water-based and solvent epoxies lose their water or solvent as they cure. Only the volume solids stay on the floor, so the same gallon covers 1604 × solids ÷ mils: a 50 % solids product at 3 mils dry covers about 267 ft². That is why the coverage on the label, at the thickness the maker means, is the figure to use for those products.
Garage floor epoxy example
A 20 ft × 20 ft garage is 400 ft². Two coats of a 100 % solids epoxy at 10 mils (160.4167 ft²/gal per coat) take 4.99 gal; with 10 % spare that is 5.49 gal — 6 one-gallon kits.
Tips before you buy
- Mix only what you can roll out within the pot life — epoxy left in the bucket hardens and is wasted.
- Work in good light and keep a wet edge: roll in 4 × 4 ft sections and back-roll across.
- Check the temperature range on the label. Cold slabs cure slowly and can blush; hot ones shorten the pot life.
- Decorative flakes and anti-slip grit are broadcast into the wet coat; their makers give how many pounds per 100 ft².
- Hot tires can lift thin coatings: a thicker 100 % solids system or a polyaspartic topcoat stands up to cars better.
Frequently asked questions
How much epoxy do I need for a two-car garage?
A 20 × 20 ft garage is 400 ft². At 10 mils, a 100 % solids epoxy covers 160 ft² a gallon, so two coats take about 5 gallons, or 5½ with 10 % spare. A thinner water-based product goes further: use its label coverage.
How many square feet does a gallon of epoxy cover?
It depends on the thickness and the solids. A 100 % solids epoxy covers 1604 ÷ mils ft²: 267 ft² at 6 mils, 160 ft² at 10 mils, 107 ft² at 15 mils. A product with 50 % solids covers half as much at the same dry thickness.
How thick should a garage floor epoxy be?
Follow the system's data sheet. Thin water-based kits go on at a few mils a coat; 100 % solids coatings are usually built to 10 mils or more in total. More thickness means more protection and more material.
Why add spare?
Bare concrete soaks up part of the first coat, rollers and trays hold epoxy, and mixed epoxy can't be saved. About 10 % covers a smooth, sound slab; rough or very porous concrete needs more.
What is the difference between mils and microns?
One mil is a thousandth of an inch, 25.4 µm. So 10 mils is 254 µm, and 250 µm is about 10 mils.
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Sources
- Coating coverage calculations: theoretical coverage = 1604 × volume solids ÷ dry film thickness (mils)
- Spartan Chemical – Concrete mil thickness and coverage
- NIST Handbook 44, Appendix C – US gallon = 231 in³ (exact)
Formulas last reviewed: September 30, 2026 ·How we check our formulas