How to measure a floor for epoxy
Measure the length and width of the slab, wall to wall, and go past any step or apron you mean to coat. Cut-outs for a water heater or a set of stairs are usually too small to count, so leave them in and keep the small extra as your margin.
The number that matters more is on the tin. Coverage changes a lot between products, and a kit is not a gallon: Rust-Oleum's water-based kit holds 90 fluid ounces of base and 30 of activator, and says it covers about 250 square feet. Griot's says a gallon covers 200 to 350 square feet in a single coat. Read yours, and enter that figure.
Then look at the slab itself. ArmorGarage says that quality, porosity and density vary greatly between floors, and cause differences in coverage of up to 20 percent. The calculator takes that 20 percent off when you mark a slab porous. It is a seller's upper limit and not a measurement, so you can use the low end of your label's range instead.
A worked example
Griot's uses a 20 by 24 foot floor as its average two-car garage, so here it is with a one coat kit. These lines come from the same formula the calculator above runs.
24 by 20 ft floor, one coat, 250 sq ft a kit
- 24 × 20 = 480 sq ft
- 480 × 1 ÷ 250 = 1.92 kits
- Buy 2 kits
- On a porous slab, 480 × 1 ÷ 200 = 2.40, so buy 3
For Griot's 2 coat system, the sum gives 2.74 to 4.80 gallons from its printed coverage. Its sheet says 3 to 4 gallons for this floor, which is a little narrower than the arithmetic. If the slab still needs pouring, the concrete calculator gives you the yards, and the garage cost calculator prices a new one.
Epoxy by garage floor size
These show how far apart two products can be on one floor. The floor sizes are examples, so measure yours. 200 and 350 are Griot's two ends for a gallon in one coat.
| Floor | Area | One coat at 250 | Two coats at 200 | Two coats at 350 |
|---|---|---|---|---|
| One car, small, 20 × 10 ft | 200 sq ft | 1 | 2 | 2 |
| One car, 24 × 12 ft | 288 sq ft | 2 | 3 | 2 |
| Two cars, small, 20 × 20 ft | 400 sq ft | 2 | 4 | 3 |
| Two cars, 24 × 20 ft | 480 sq ft | 2 | 5 | 3 |
| Two cars, deep, 24 × 24 ft | 576 sq ft | 3 | 6 | 4 |
| Three cars, 30 × 24 ft | 720 sq ft | 3 | 8 | 5 |
Mistakes when buying epoxy
- One coat of coverage for two coats. A kit's figure is usually for a single coat. Griot's 200 to 350 becomes 100 to 175 at 2 coats.
- A one car kit on a two car floor. Sherwin-Williams' kit covers 200 to 250 square feet, or one car. A two-car floor is about twice that.
- Mixing too much at once. Mix one kit at a time, as pot life is short, and Valspar says not to intermix gallons.
- Skipping the moisture test. Griot's stresses testing first. Rust-Oleum says its kit is not for floors with a moisture problem.
- Coating new concrete too soon. Rust-Oleum asks for a minimum of 28 days.
Questions
How much epoxy for a two-car garage?
About 2 kits for one coat at 250 square feet a kit, on a 20 by 24 foot floor. Valspar also says 2 kits for a two-car garage. Griot's says 3 to 4 gallons for its 2 coat system on the same floor, so check your own product's sheet.
How many coats of epoxy?
One or two, as your product says. Rust-Oleum says only one coat is necessary under most circumstances for its kit. Griot's recommends a minimum of 2 for its coating, so the coverage and coat count have to come from the same sheet.
Does concrete porosity change coverage?
Yes, and ArmorGarage says by up to 20 percent from floor to floor. Sherwin-Williams gives 200 to 250 square feet a kit depending on porosity. No label we read prints a factor, so ours takes off the whole 20 percent on old slabs.
What is epoxy floor coverage per gallon?
About 200 to 350 square feet in a single coat on Griot's sheet, which comes to 100 to 175 at its 2 coats. Valspar gives about 200 over smooth concrete. These differ between products, so use the figure printed on yours.
How much epoxy flake do I need?
Follow the amount on your kit's label, because we could not find a rate in pounds per square foot from a source we could read. Kits vary in size, so we do not work out a figure here rather than guess one for you.
Can I coat new or damp concrete?
Not until it is cured and dry. Rust-Oleum asks for a minimum of 28 days on new concrete, and says its kit is not for floors with a moisture problem. Griot's stresses testing for moisture and hydrostatic pressure first.
This epoxy quantity is an estimate from the coverage you enter, so use the figure on your own product's label. Concrete porosity and density change coverage from floor to floor, and one maker's range does not fit another's. Data sheets assume a sound, etched, dry slab, and no calculator can detect moisture rising through it, so test first.
Sources and review
- Waterborne epoxy garage floor coating data sheet, Rust-Oleum, no date printed, file details 2010.
- Industrial epoxy floor coating data sheet, Griot's Garage, 2021.
- Epoxy garage floor specification sheet, Valspar, 2012.
- H&C Shield-Crete water-based epoxy, Sherwin-Williams, no date shown, read November 2026.
- Armor Chip garage epoxy floor kits, ArmorGarage, no date shown, read November 2026.
Checked in November 2026. Spotted a wrong number? Report it and it goes in the corrections log.
How this is calculated
Every figure below is read from the code that produces the answer, so what is written here is what the calculator ran. The constants were last checked against their sources in November 2026.
The arithmetic
Epoxy
Amount = Area × Coats ÷ Coverage
- Coverage
- Square feet per kit or gallon for one coat, from your label
Worked through: 480 × 1 ÷ 250 = 1.92
Porous slab
Coverage used = Label coverage × 0.8
- 0.8
- Keeps 80 percent, from a seller's limit of up to 20 percent
Worked through: 250 × 0.8 = 200
The constants, and where they come from
DEFAULT_COVERAGE_SQ_FT
Published range, narrowedStarting coverage for one coat, per kit, in square feet
Applies to: Rust-Oleum's water-based kit. Every product differs, so the field takes your label
Source: Waterborne epoxy garage floor coating data sheet, Rust-Oleum, no date on the page, read 2026-11.
Also from: Industrial epoxy floor coating data sheet, Griot's Garage, published 2021-09, read 2026-11.
Also from: Epoxy garage floor specification sheet, Valspar, published 2012-09, read 2026-11.
Also from: H&C Shield-Crete water-based epoxy, Sherwin-Williams, no date on the page, read 2026-11.
An old sheet, with file details from 2010. Griot's prints 200 to 350 per gallon, Valspar about 200 per gallon on smooth concrete and Sherwin-Williams 200 to 250 per kit.
POROUS_COVERAGE_FACTOR
Modelled from published dataCoverage kept on a porous slab, as a share
Applies to: Our reading of a seller's upper limit, for an old porous slab
Source: Armor Chip garage epoxy floor kits, ArmorGarage, no date on the page, read 2026-11.
No label prints a percentage factor. ArmorGarage says differences of up to 20 percent, and we take the whole of that. Using the low end of your label's range also works.
What the labels mean
- Published range, narrowed:
- a source publishes a range and this calculator uses a representative value from it.
- Modelled from published data:
- derived rather than measured, calibrated against the source named beside it.
If a figure here looks wrong, it may be. Tell us what you found and we will check it against the source and publish a correction if it needs one. How constants are chosen and how often they are reviewed is set out in our methodology.
How to use the epoxy floor calculator
- 1
Measure the floor
- 2
Read the coverage from your product
- 3
Enter the coats its label asks for
- 4
Say if the concrete is old or porous
- 5
Mix one kit at a time when you start the job
What this calculator assumes
Every estimate here rests on the assumptions below. Where your job differs from one of them, the figure will differ too.
- Each coat spreads the same, which Griot's sheet prints and not every product does
- A porous slab loses 20 percent of its coverage, taken from a seller's upper limit
- Amounts are rounded up to whole kits or gallons
Pro tips
- Mix one kit at a time, as Valspar warns against intermixing gallons
- Keep the coverage and coats from the same sheet
- Use the low end of your label's range on an old slab