An epoxy coating turns a dusty, stained concrete garage floor into a smooth surface that resists oil, salt and hot tires. Most products are sold in kits that cover a stated area per coat. This calculator works out how much epoxy and primer you need, how many kits to buy and what the project costs.
The formula
- Epoxy (gal) = floor area × number of coats ÷ coverage per gallon
- Kits = epoxy needed ÷ kit size, rounded up
- Primer (gal) = floor area ÷ primer coverage
Example
A 400 sq ft two-car garage with two coats at 250 sq ft per gallon needs 3.2 gallons of epoxy: 4 one-gallon kits. A primer coat at 300 sq ft per gallon needs 1.3 gallons, so 2 cans. At $120 a kit and $50 a can, the project costs $580, about $1.45 per sq ft.
Coverage by product
| Product | Typical coverage per coat |
|---|---|
| Water-based epoxy kit | 250 to 300 sq ft per gallon |
| Solvent-based epoxy | 200 to 250 sq ft per gallon |
| 100% solids epoxy | 120 to 160 sq ft per gallon (thicker film) |
| Polyurea or polyaspartic topcoat | 200 to 400 sq ft per gallon |
Rough or porous concrete absorbs more product: reduce the coverage by 10 to 20% for an old, worn slab.
Garage sizes
| Garage | Typical floor area |
|---|---|
| One car | 200 to 250 sq ft |
| Two cars | 400 to 480 sq ft |
| Three cars | 600 to 750 sq ft |
Preparation is everything
Most epoxy failures come from poor surface preparation, not from the product.
- Remove oil stains with a degreaser.
- Etch the concrete with an acid etch or, better, grind it, so the epoxy can grip.
- Repair cracks and holes with an epoxy filler.
- Tape a plastic sheet on the floor for 24 hours: if moisture appears under it, the slab is too damp to coat.
- Apply in the temperature range on the label, usually 50 to 90 °F.
Most kits allow foot traffic after about 24 hours and cars after about 72 hours; full cure can take a week. Decorative flakes add grip and hide imperfections; a clear topcoat makes the surface more durable.
Safety
Ventilate well, wear gloves and eye protection, and check the label for respirator requirements, especially with solvent-based products.