Understanding your result
The headline is the floor coating for the coats the product needs, with the allowance, and the sub-line gives the cans and the etch. The three figures show the floor area, the real coverage after the surface factor and the cans.
The table shows the area, the product with its typical or your can’s coverage, the concrete surface factor, then the usual coverage, coats, per-coat, allowance, total and can lines, and finally the etch units and the primer if you ticked them. The shopping list puts the coating, the etch and the primer together.
Concrete is the one surface where the choice of product matters as much as the quantity. The epoxy kit calculator covers two-part systems with flakes and topcoat; the porch floor calculator covers porches and patios; the masonry sealer calculator covers clear penetrating sealers on brick and pavers; and the block filler calculator covers concrete block walls.
How we calculate this
The product coverages are the typical figures on floor coating data sheets for smooth, prepared concrete: about 300 sq ft per gallon for one-part epoxy floor paint, 350 for acrylic floor paint and 250 for a clear sealer, each at two coats. Rough and porous slabs take more because the profile adds surface and the pores absorb the first coat; the factors are the ratio of the data sheets’ rough-surface figures to their smooth ones. The coverage rates table lists the ranges and the coverage guide explains the porosity.
The etch figure is the typical label coverage of a concrete etch, about 250 sq ft per bag or per gallon of mixed solution. The moisture test is ASTM D4263, the standard plastic-sheet method. The drying and cure guide covers the wait before vehicles.
The assumptions behind the numbers
| Assumption | Default | Where it comes from |
|---|---|---|
| One-part epoxy floor paint | 300 sq ft per gallon, 2 coats | Floor coating data sheets (Rust-Oleum, Behr, Valspar, Sherwin-Williams): 300–400 |
| Acrylic floor paint | 350 sq ft per gallon, 2 coats | The same sheets |
| Clear sealer | 250 sq ft per gallon, 2 coats | Concrete sealer data sheets: 200–300 |
| Surface factors | smooth 1.0, rough 0.8, porous 0.7 | Ratio of rough to smooth coverage on the sheets |
| Etch | 250 sq ft per unit | Typical concrete etch label coverage |
| Concrete primer | 300 sq ft per gallon | Concrete primer data sheets: 250–400 |
| Moisture test | plastic sheet, 24 h | ASTM D4263 |
Assumptions last reviewed October 8, 2026.
The calculator does not model grinding, which is the professional alternative to etching, crack and spall repair, oil-stain removal, or new concrete, which must cure about 28 days before coating. It does not cover two-part systems, which have their own calculator.
Two worked examples
A two-car garage in one-part epoxy
24 × 22 ft, smooth troweled slab never coated, two coats at 300 sq ft per gallon, etched.
- Area: 24 × 22 = 528 sq ft
- Per coat: 528 ÷ 300 = 1.76 gallons
- Coating: 1.76 × 2 × 1.05 = 3.7 gallons, buy 3 gallons + 3 quarts
- Etch: ⌈528 ÷ 250⌉ = 3 units
In metric the same floor, 7.3 × 6.7 m, is 48.9 m² and 14 litres, a 10 L and a 5 L can.
A broom-finished basement floor in acrylic, primed
Same area, acrylic floor paint, rough concrete, already etched, a primer coat.
- Real coverage: 350 × 0.8 = 280 sq ft per gallon
- Coating: 528 ÷ 280 × 2 × 1.05 = 3.96 gallons, buy 4 gallons
- Primer: 528 ÷ 240 × 1.05 = 2.31 gallons, buy 2 gallons + 2 quarts
The primer is nearly as much as a coat of paint, which is normal on a porous slab and the reason the second coat looks even.
Where to find your inputs
Length and width. The floor, wall to wall; subtract only large fixed obstacles.
Product. On the can: one-part epoxy, acrylic or latex floor paint, or sealer.
Concrete. Smooth and shiny is troweled; textured with fine lines is broom-finished; dusty, pitted or stained is porous.
Etch and primer. Etch bare concrete; prime porous or patched slabs and where the data sheet asks for it.
Common mistakes
- Skipping the moisture test. Moisture from below lifts every coating.
- Painting over oil stains. Degrease until water no longer beads on the spot.
- Not etching smooth concrete. The paint peels in sheets.
- Driving on it too soon. Hot tyres lift uncured paint; wait the full time on the can.
- Applying in the cold. Most floor coatings need 50 °F (10 °C) or more in the slab, not just the air.
- One-part paint where a two-part epoxy was needed. Heavy vehicles and chemicals need the harder system.
Questions people ask
- How much paint does a garage floor need?
- A 24 × 22 ft two-car garage is 528 sq ft. One-part epoxy floor paint at about 300 sq ft per gallon on smooth concrete takes 1.76 gallons per coat; two coats with a 5% allowance is 3.7 gallons, so three gallons and three quarts, plus about three units of etch.
- What is the difference between epoxy floor paint and an epoxy kit?
- One-part epoxy floor paints are acrylics with some epoxy added. They come in a single can, are easy to apply and forgiving, but softer. Two-part epoxy kits are mixed from resin and hardener, cure much harder and resist hot tyres and chemicals, but have a short pot life. The epoxy kit calculator covers those.
- Do I have to etch concrete before painting?
- Bare, smooth concrete that has never been coated, yes, or grind it. Etching opens the surface so the coating can grip. A previously coated floor that is sound needs cleaning and scuffing instead. Sealed or oil-stained concrete needs degreasing and testing first.
- How do I test a slab for moisture?
- Tape an 18 in square of clear plastic to the floor on all four edges and leave it 24 hours, which is the ASTM D4263 plastic-sheet test. If the concrete under it darkens or droplets form, moisture is coming up and a coating will blister and lift.
- How much does rough concrete reduce coverage?
- A broom-finished or rough slab takes about 20% more paint than a smooth, troweled one; an old, porous or never-sealed slab about 30% more. The calculator multiplies the can's coverage by 0.8 or 0.7.
- How long before I can drive on it?
- Most one-part floor paints allow foot traffic after a day and vehicles after about a week; check the can. Hot tyres on paint that has not cured are the most common cause of peeling.