Floor coatings are specified by thickness, measured in mils (thousandths of an inch). One US gallon is 231 cubic inches, so spread 1 mil thick it covers 1,604 ft². Divide that by the film thickness you want and adjust for the coating's solids, the part that stays after the solvent or water evaporates, and you have the true coverage. This epoxy floor calculator uses that rule to give gallons and kits for a garage, basement or shop floor. A 24 × 24 ft two-car garage at 10 mils dry with 100% solids epoxy needs about 4 gallons per coat with 10% extra.
Coating a new slab? It should cure fully first; the concrete slab calculator covers the pour. Painting walls in the same space? Use the paint calculator.
How to use the epoxy floor coating calculator
- Enter the floor length and width. Measure into bays and around steps separately and use the square footage calculator for odd shapes.
- Choose the number of coats: a primer, a body coat with flakes and a clear topcoat are common in professional systems. Run each product separately if their thickness or solids differ.
- Enter the dry film thickness per coat from the product data sheet. Consumer kits are often thin (a few mils); professional 100% solids systems are often 8 to 20 mils.
- Enter the volume solids. Solvent-free epoxies are close to 100%; water-based kits are much lower, so they cover more area at a thinner dry film.
- Keep 10% or more extra for porous concrete, roller absorption and mixing loss.
Formula
1,604 comes from 231 in³ per gallon ÷ (0.001 in × 144 in² per ft²) = 1,604.2 ft².
Worked example
A 24 × 24 ft garage, one coat at 10 mils dry, 100% solids epoxy, 10% extra, sold in 1 gallon units.
- Area: 24 × 24 = 576 ft².
- Coverage: 1,604 × 1.00 ÷ 10 = 160 ft² per gallon.
- Gallons: 576 ÷ 160.4 × 1.10 = 3.95 gallons, so 4 gallons.
With a water-based kit at 50% solids applied at 3 mils dry, coverage would be 1,604 × 0.5 ÷ 3 = 267 ft² per gallon, and the same floor would take about 2.4 gallons per coat, but the finished film would be less than a third as thick.
Coverage by film thickness and solids
Theoretical coverage per gallon per coat, before waste.
| Dry film per coat | 50% solids | 70% solids | 100% solids |
|---|---|---|---|
| 3 mils | 267 ft²/gal | 374 ft²/gal | 535 ft²/gal |
| 5 mils | 160 ft²/gal | 225 ft²/gal | 321 ft²/gal |
| 8 mils | 100 ft²/gal | 140 ft²/gal | 201 ft²/gal |
| 10 mils | 80 ft²/gal | 112 ft²/gal | 160 ft²/gal |
| 15 mils | 53 ft²/gal | 75 ft²/gal | 107 ft²/gal |
| 20 mils | 40 ft²/gal | 56 ft²/gal | 80 ft²/gal |
Epoxy for common garage sizes
| Garage | Area | Gallons, 1 coat at 10 mils, 100% solids, +10% |
|---|---|---|
| 1-car (12 × 22 ft) | 264 ft² | 1.81 |
| 2-car (20 × 20 ft) | 400 ft² | 2.74 |
| 2-car (24 × 24 ft) | 576 ft² | 3.95 |
| 3-car (32 × 24 ft) | 768 ft² | 5.27 |
Garage dimensions vary; measure yours.
Prep makes or breaks it
Coating failures are usually preparation failures. Coatings bond best to clean, dry concrete with an open surface profile, typically achieved by diamond grinding or shot blasting; acid etching is common with consumer kits. Test for moisture before coating; concrete that is wet underneath can push the coating off. Repair cracks first, follow the mixing ratio and pot life exactly, and keep within the temperature range on the label. The coatings industry's professional body, AMPP (formerly SSPC and NACE), publishes surface preparation standards, and kit makers such as Rust-Oleum list their own prep steps and coverage per kit. For asphalt rather than concrete, use the driveway sealer calculator.
Caveats and assumptions
- This is theoretical coverage. Rough or porous concrete, textured flakes and rollers absorb extra material.
- Consumer kits often list coverage per kit directly; when they do, compare it with the result here and use the more conservative number.
- Primers, body coats and topcoats usually have different thickness and solids. Calculate them separately.
- Epoxy has a short pot life. Mix only what you can apply in time.
Frequently asked questions
How much epoxy do I need for a 2-car garage?
For a 24 × 24 ft garage (576 ft²) at 10 mils dry with 100% solids epoxy, about 3.6 gallons per coat before waste, or 4 gallons with 10% extra.
How many square feet does a gallon of epoxy cover?
A gallon covers 1,604 ft² at 1 mil wet. At 10 mils, 100% solids epoxy covers about 160 ft² per gallon; at 5 mils about 320 ft².
What is a mil of epoxy?
One mil is one thousandth of an inch (0.0254 mm). A typical professional garage coating system totals roughly 15 to 30 mils across all coats.
What does volume solids mean?
It is the share of the liquid that remains as cured film. At 50% solids, a 6 mil wet film dries to 3 mils, so you need twice the wet thickness to reach the same dry film.
How many coats of epoxy on a garage floor?
Many systems use a primer or base coat, an optional broadcast of decorative flakes, and a clear topcoat. Follow the product system instructions.
Sources
- NIST — Handbook 44 (unit equivalents) — 1 US gallon = 231 cubic inches
- AMPP (Association for Materials Protection and Performance) — coating thickness and surface preparation standards
- Rust-Oleum — EpoxyShield garage floor coating kit — example consumer kit coverage and preparation steps
This calculator gives estimates for planning and education. Check measurements, local codes, supplier specs and your school's official policy before relying on a result. See our disclaimer and how we build and check calculators.