Garage floor epoxy calculator

Garage floor kits are sold by the square feet they cover, not by volume. Buying floor epoxy by the gallon from a coatings supplier? Use the floor coating calculator. Words on the box you don’t know? See epoxy words explained.

How the kit count is worked out

Kits are rated in square feet per coat, so the math is simple: floor area × coats, plus a margin for porous concrete and roller losses, divided by the coverage on the box. The count is always rounded up — you can’t buy 1.4 kits, and running out halfway across a floor leaves a lap mark.

area = length × width
coverage needed = area × coats × (1 + waste)
kits = coverage needed ÷ kit coverage (round up)

A 20 × 20 ft two-car garage is 400 sq ft. With one coat and 10% waste you need 440 sq ft of coverage. With kits rated at 250 sq ft that’s 1.76 — so two kits. The worked examples go through the common sizes: How much epoxy for a 1-car garage floor, How much epoxy for a 20×20 two-car garage, How much epoxy for a 24×24 garage floor (with a full flake broadcast), How much epoxy for a 3-car garage floor and, in metric, How much epoxy for a 3 × 6 m single garage.

Kit coverage varies a lot

Coverage claims on garage floor kits range widely — from roughly 250 sq ft to 500 sq ft or more per box — because kits differ in how much material they contain and how thick they’re meant to go on. Water-based epoxy kits tend to be rated for larger areas at a thinner film; 100%-solids systems go on thicker and cover less per gallon. Spartan Epoxies, for example, lists its floor coating at about 133 sq ft per gallon at 12 mils (thousandths of an inch) and about 267 sq ft at 6 mils — halve the film, double the coverage. Use the number printed on the kit you’re actually buying, and note whether it’s per coat. If you’re buying coatings by the gallon rather than as kits, the epoxy floor coating calculator works from film thickness or the data sheet’s coverage rate instead.

Decorative flakes

Flakes (chips) are broadcast into the wet base coat. A light sprinkle uses very little; a full broadcast “to rejection” — throwing chips until the wet coat can’t hold any more — covers the floor completely and uses a lot more. Published figures vary with chip size and how you throw: Concrete Floor Supply plans on about 0.10 lb per sq ft for 1/4 in chips and 0.20 lb for 1/8 in chips at full coverage, and WALT Tools plans on about 8 sq ft per pound (roughly 0.125 lb per sq ft) while noting real use runs from about 5 to 10 sq ft per pound. The calculator uses 0.15 lb per sq ft for a full broadcast — change it under More options for your chip size — about 5 lb per 100 sq ft for a partial broadcast where the base color still shows, and about 1.5 lb per 100 sq ft for a light sprinkle.

Chips are sold by weight, and full floors are usually bought in 40 lb boxes, so the calculator rounds the weight up to whole boxes. Buy one blend from one supplier, in one order, so the color is the same across the floor. Once the base coat has cured, the loose chips are scraped and swept off; most full-chip floors then get a clear topcoat — see the floor coating calculator if you’re buying that topcoat by the gallon, with a primer, or with a cove base up the walls.

Before you buy

• Measure the floor, not the garage door count — “two-car” garages range from about 18 × 20 ft to 24 × 24 ft.
• Leave out areas under fixed cabinets or workbenches you won’t move.
• Buy all kits from the same batch if the color matters.
• Test for moisture first. Garage Flooring LLC’s instructions describe taping down a 24 in square of plastic sheet for 24 hours; condensation underneath means the slab isn’t ready to coat.
• Check the slab temperature, not just the air: a cold slab slows the cure. The cure time calculator adjusts the label times.
• Ventilate while you work. The EPA advises increasing ventilation when using products that release volatile organic compounds (VOCs), which many floor coatings do.
• Prep is most of the job. See the garage floor epoxy guide for cleaning, moisture testing and etching or grinding.