Epoxy Floor Calculator

Every epoxy floor calculator asks for an area and answers in gallons. The gallons are the easy part and they are not what goes wrong.

What goes wrong is the slab, and the manufacturer says so before it says anything about coverage:

Testing must be performed to confirm a moisture vapor emission rate below 20 lb/24hr/1000 ft2 per ASTM F1869 or between 75% and 95% for ASTM F2170.

Three of those are measurements somebody has to take, and two of them take days. A calcium chloride test sits on the slab for 60 to 72 hours. An in-slab relative humidity probe needs 72 hours to equilibrate in the hole. Neither is expensive and neither is optional if you want the coating to stay on.

Read the humidity row twice. It is a range, not a maximum: 75% to 95%. A slab can be too dry for this product as well as too wet.

And the sheet is blunt about what the product will not fix:

Product will not prevent failures from insufficient surface preparation, improper applications, alkaline silica reaction (ASR), iconic compounds or soluble salts in the concrete.

Coat a slab that fails the vapour test and the coating lifts, months later, in sheets. No amount of grinding prevents it, because the water is arriving from underneath.

Once Part A and Part B are mixed the reaction is running. On this product the pot life is 25 to 38 minutes at 70 degrees, and it is shorter in a warm garage because the reaction is exothermic and a bigger batch holds its own heat.

So the question is not how much you can carry. It is how much floor you can cover before the bucket sets. At 90 to 94 square feet per gallon a 3 gallon kit is 270 to 282 square feet to spread in half an hour.

That is the number to plan a garage floor around. A two-car garage is around 400 to 500 square feet, so it is not one batch, it is two or three, and each one has to be started, spread and back-rolled into the previous one before that one has gone off.

And the mix ratio is 2 parts A to 1 part B by volume, which means you cannot make a half batch by eye. Part-mixing a kit is measured, not estimated, and a batch that is off ratio does not cure: it stays soft, permanently, and has to come off.

Two people is the practical answer on anything larger than a single bay. One mixes and keeps the next batch coming, one spreads.

Coverage figures on a data sheet assume a prepared surface, and preparation on concrete means profile rather than cleanliness.

A sealed or troweled slab has nowhere for the epoxy to key into. Acid etching, diamond grinding and shot blasting all open the surface, and they do not produce the same profile as each other. The data sheet for your product will name what it wants.

Anything left on the slab defeats it. The sheet read for this page is explicit that the product will not prevent failures from insufficient surface preparation, improper application, alkaline silica reaction or soluble salts in the concrete. Oil in a garage floor is the common one, and it has usually been there for years and gone in deep.

Preparation also changes the coverage. A ground slab is rougher than a troweled one and the first coat has more surface to cover, so the published figure is a best case. That is what the waste allowance on this page is for, and it is ours rather than the manufacturer's.

The calculator takes a coat count because the answer scales with it, and the decision is not only about durability.

A second coat is a second full quantity of product, at the same coverage, unless the sheet says otherwise. It is not a touch-up.

Decorative flake changes the topcoat, not the base. Flake is broadcast into the wet base coat and then locked down with a clear topcoat, which is a third full application. A flake floor is base plus clear at minimum, and the clear is usually a different product with its own coverage and its own pot life.

And every extra layer is another pot life to work inside. The clock restarts with each batch of each coat, and the recoat window between them is on the sheet: on the product read for this page it is 11 to 16 hours, so the second coat is the next day and not the same evening.

Run this page once per product rather than trying to make one coverage figure describe a base and a clear.

This product is 100% solids by volume, so what you spread and what is left when it cures are the same thickness. That makes it the cleanest possible test of a relationship this site sets out on the paint calculator: a US gallon is 231 cubic inches, so spread one mil thick it covers 1,604 square feet, and every published coverage figure is that number divided by the film thickness printed beside it.

1,604 / 94 sq ft per gal = 17.1 mils    1,604 / 90 = 17.8 mils

The sheet prints a recommended film thickness of 17 to 18 mils. The two agree to a tenth of a mil, on a product that has nothing in common with wall paint except that it is a liquid measured in gallons.

Which is worth knowing when a coverage figure looks generous. Divide 1,604 by it and you have the film thickness the manufacturer is assuming. If that comes out at 5 mils on a product sold for a garage floor, the figure is for a sealer, not a coating.

The paint page owns the full argument and the six data sheets behind it. This is one more sheet agreeing with it from a long way away.

Application temperature on this product is 60 to 90 degrees with relative humidity below 90%. Those are the easy ones to check. The one that catches people is not a temperature at all:

Substrate temperatures must be 5°F above dew point.

5 degrees above the dew point, measured on the slab rather than in the air. A concrete floor lags the air temperature by hours and sometimes days, so on a mild morning after a cold night the slab can be below the dew point while the garage feels fine. Coat it then and there is condensation under the epoxy before it cures.

An infrared thermometer settles it in seconds and costs less than a gallon of the product. Take the slab temperature, take the air temperature and humidity, work out the dew point, and if the gap is under five degrees, wait.

This is also why spring and autumn garage floor jobs fail more often than summer ones, and why the failure is blamed on the product.

Read 2026-09-10. Technical Data, FGP MV 2112, 100% Solids Epoxy Moisture Vapor Barrier, Floorguard Products, manufacturer technical data sheet. Publishes coverage, recommended film thickness, mix ratio, pot life and the four substrate conditions that have to be met before the product may be applied, including a moisture vapour emission rate test and a slab relative humidity test.

Every figure on this page belongs to one product. The coverage, the film thickness, the pot life, the mix ratio and all four substrate gates are that manufacturer's, for that epoxy, and another product will have its own. The calculator takes yours as inputs and defaults to these so there is something to look at.

What generalises is the shape of it. Every two-part epoxy has a pot life, a mix ratio and substrate conditions, and every one of them publishes them, because a coating that fails on a wet slab is a warranty claim. Find your product's sheet before you buy the kit, not after.

The two test methods are ASTM standards and are not free documents. They are named here because the data sheet names them; the numbers quoted are the manufacturer's limits, not the standards' contents. A concrete testing firm will run either for a few hundred dollars, which is cheap against recoating a garage.