How the calculator works
Epoxy is a coverage problem: every product lists square feet per gallon at its recommended film thickness. The math is simply:
Gallons = (area × coats) ÷ coverage per gallon, plus 10% because running out mid-floor leaves a visible lap line you cannot blend later.
Worked example: a 440 sq ft two-car garage getting two coats at 250 sq ft/gal needs 3.5 gallons, so buy about 3.9 with the margin, which is one 3-gal kit plus a 1.5-gal kit, and keep the spare part-kit for touch-ups.
What actually determines success
Epoxy failures are almost never about the epoxy. They're about prep. Budget your time accordingly:
- Moisture test first: tape a 2×2 ft plastic square to the slab for 24 hours. Condensation underneath means moisture is migrating up and epoxy will peel; you need a moisture-tolerant primer or a different floor.
- Profile the surface: etch with the kit's acid wash or, better, rent a diamond grinder. Epoxy needs tooth and will not bond to smooth, sealed, or painted concrete.
- Degrease twice: oil spots that survive cleaning become fish-eyes in the finish.
- Watch the pot life: once mixed, a kit gives you 30–60 minutes. Mix one kit at a time and have your roller path planned.
Kit sizing
Retail "one-car" kits typically contain about 1.5 gallons and claim 250 sq ft; "two-car" kits about 3 gallons. Claims assume one thin coat on smooth concrete. Real two-coat jobs on ground concrete need roughly double the kit label's promise, which is what this calculator accounts for.