Epoxy Floor Coating Calculator
Gallons of epoxy for a garage or basement floor, by coats.
Most floors get a primer or base coat plus a top coat.
From the kit. Water-based: 200 to 300. 100% solids: 80 to 100.
You need
3.2 gallons
Round up to whole kits. Mixed epoxy cannot be saved for later.
- Floor area
- 400 sq ft
- Total area to coat
- 800 sq ft
Estimates only. Verify quantities before ordering.
How this is calculated
Gallons = floor area x coats / coverage per gallon. A standard 2-car garage is about 400 to 500 sq ft; check your kit's stated coverage and buy whole kits.
Enter the floor dimensions, the number of coats, and the coverage rate from your product, and this calculator returns the gallons to buy. Epoxy is usually sold as two-part kits sized in half-gallon and gallon units of mixed product, and the box states its coverage for one coat, which is the number to enter here.
Coverage varies by chemistry more than any other coating. Water-based epoxy paints spread thin and cover 200 to 300 square feet per gallon, while high-build 100% solids epoxies go on thick and may cover only 80 to 100. Rough or porous concrete drinks more in the first coat, and broadcast color flakes or anti-slip grit do not change the liquid math.
Epoxy for common floor sizes
Rows assume two coats at 250 sq ft per gallon. Round up to whole kits.
| Floor | Gallons | Area |
|---|---|---|
| 12 x 22 ft (1-car garage) | 2.1 gallons | 264 sq ft |
| 20 x 20 ft (2-car garage) | 3.2 gallons | 400 sq ft |
| 24 x 24 ft (large 2-car) | 4.6 gallons | 576 sq ft |
| 30 x 24 ft (3-car garage) | 5.8 gallons | 720 sq ft |
| 30 x 40 ft (shop floor) | 9.6 gallons | 1,200 sq ft |
Solids content is what you are buying
Epoxy is sold by volume, but what matters is the percentage of solids, meaning what remains after the carrier evaporates. A 100 percent solids epoxy leaves behind essentially everything in the can and builds a film measured in tens of mils, which is what commercial floors use. It also cures fast, gives you a short working window, and is unforgiving of a poor mix.
Water-based and solvent-based epoxies typically run 40 to 60 percent solids. They go on thinner, penetrate better, cost less, and are much easier for a first-timer to spread evenly, but a single coat is a fraction of the thickness of a high-solids product. The kits sold at home centers are usually in this category, which explains why their coverage per gallon looks so generous and why they wear through sooner in a working garage.
Compare products on coverage at a stated thickness rather than on price per gallon. A cheaper gallon covering twice the area is laying down half the film, and film thickness is most of what determines how long the floor survives hot tires, dropped tools, and road salt.
Preparation decides whether it sticks
Nearly every failed garage floor coating failed at the bond, not in the epoxy. Concrete has to be clean, free of any previous sealer, and mechanically profiled so the coating has something to key into. Grinding with a diamond cup wheel is the reliable method; acid etching is the common shortcut and works only on bare, absorbent concrete, and it frequently leaves the surface too smooth where the concrete was dense or burnished.
Test for absorbency before anything else. Sprinkle water on several spots: if it beads rather than soaking in within a minute, there is a sealer or a densifier present that must be removed. Also test for moisture coming up through the slab by taping a couple of feet of plastic sheet down for 24 hours and checking underneath for condensation. Vapor drive from below will lift a coating off an otherwise perfect floor, and it needs a moisture-tolerant primer.
Fill cracks and spalls with an appropriate patching compound and let them cure fully, and vacuum rather than sweep at the end. Dust left in a profiled surface acts as a bond breaker in exactly the places you worked hardest to prepare.
Working time, coats, and curing
Two-part epoxy begins reacting the moment it is mixed, and pot life is short: often 30 to 45 minutes, less in a warm garage. Mix only what you can spread in that window, mix the full kit proportions precisely rather than eyeballing a partial batch, and stir long enough to combine thoroughly while scraping the sides of the bucket. Under-mixed epoxy cures soft in patches and never recovers.
Most systems want a primer or a thinned first coat, then a build coat, with decorative flake broadcast into the wet build coat if you are using it, and a clear topcoat over the flake. Respect the recoat window on the label. Going back too early traps solvent; leaving it too long means the next coat cannot chemically bond and the surface has to be abraded first.
Cure times are longer than they feel. Foot traffic is usually fine within a day, but vehicles typically need three to seven days, and driving on a floor that is walkable but not fully cured leaves permanent tire marks. Temperature drives all of this, and applying below the product minimum, often around 50 to 60 degrees, can stop the cure entirely rather than merely slowing it.
Common questions
How much epoxy for a 2-car garage?
A typical 2-car garage floor is 400 to 500 square feet. At 250 square feet per gallon that is about 2 gallons per coat, so a primer coat plus top coat needs around 4 gallons. Most brands sell a 2-car kit per coat; buy two kits for a two-coat system.
Why did my epoxy kit not cover what the box said?
Stated coverage assumes smooth, sealed concrete. Bare or acid-etched concrete absorbs a lot of the first coat, and rough-troweled or pitted floors add surface area. Plan on the low end of the stated range for the first coat; the second coat usually hits the rated number.
Do I need to etch or grind the floor first?
Yes, surface prep decides whether epoxy lasts. The concrete must be clean, dry, and profiled: diamond grinding is best, acid etching is the common DIY route. Test for moisture by taping down a plastic square overnight; condensation underneath means the slab needs a moisture-tolerant primer or should not be coated.
What is the difference between epoxy paint and real epoxy?
One-part 'epoxy paints' are latex with a small epoxy additive: cheap, thin, and short-lived under tires. True two-part epoxy cures chemically after you mix resin and hardener, builds a much thicker film, and resists hot-tire pickup. The two-part product is what the coverage numbers here assume.