How much epoxy for a garage floor
| Garage | Typical size | Area | 1-gal kits, smooth | 1-gal kits, porous | 100% solids at 10 mils |
|---|---|---|---|---|---|
| 1-car | 12 × 22 ft | 264 sq ft | 2 | 2 | 1.7 gal |
| 2-car | 20 × 20 ft | 400 sq ft | 2 | 3 | 2.5 gal |
| 2-car, deep | 24 × 24 ft | 576 sq ft | 3 | 4 | 3.6 gal |
| 3-car | 32 × 22 ft | 704 sq ft | 3 | 5 | 4.4 gal |
Per coat. Kit counts use about 250 sq ft per gallon on smooth, sealed-looking concrete and 160 on rough, porous concrete — the middle of the 125–200 range on Rust-Oleum's kit labels. Measure your floor rather than trusting the "2-car" on the box: garages vary a lot, and a kit that covers a 20 × 20 ft garage won't cover a 24 × 24.
Epoxy coverage calculator: the 1,604 rule
Professional coatings are specified by film thickness in mils (thousandths of an inch), and the coverage comes from simple geometry: a gallon is 231 cubic inches, which spread 1 mil thick covers 1,604 sq ft. So:
Coverage = 1,604 × volume solids ÷ mils
- 100% solids epoxy at 10 mils: 1,604 ÷ 10 = 160 sq ft per gallon
- 100% solids at 15 mils (a heavier body coat): 107 sq ft per gallon
- 50% solids water-based epoxy at 5 mils dry: 1,604 × 0.5 ÷ 5 = 160 sq ft per gallon
- Clear topcoat at 4 mils: about 400 sq ft per gallon
Switch the product to Pro epoxy by mils and enter the volume solids and the thickness from the data sheet. Real-world coverage is a little lower — rollers, buckets and the texture of the slab all soak some up — so round up.
DIY kit or 100% solids?
DIY water-based kits are thin — roughly a few mils dry — easy to roll, and forgiving of a long working time. They're a cosmetic upgrade over bare concrete and suit a garage that doesn't see much hot-tire traffic.
100% solids epoxy goes on 8–15 mils thick per coat, hides more, resists chemicals and hot tires better, and gives you a short pot life — mix only what you can roll in about 20 minutes. Most pro systems add a clear topcoat, often over decorative flakes, for wear resistance.
Either way, the coating is only as good as the slab under it. Test for moisture first: tape an 18 × 18 in sheet of plastic to the floor for at least 16 hours (the ASTM D4263 method); if the underside is wet or the concrete has darkened, moisture is coming through and the epoxy will peel. Then grind or acid-etch until the surface feels like medium-grit sandpaper, and fill cracks before you coat. If the slab is badly out of level, fix that first with the self-leveling concrete calculator; pouring a new garage slab instead? The slab calculator sizes the concrete.
