Epoxy Resin Calculator

Gallons of epoxy for river tables, countertops, and garage floors. Updated for 2026.

Last reviewed July 2026 · Free · Nothing you enter is stored

How this calculator works

Volume math: one gallon is 231 cubic inches, which covers 1.604 sq ft at 1 inch thick — so gallons = area × thickness ÷ 1.604. That's 12.8 sq ft per gallon at 1/8" and 25.6 at 1/16". Garage floor epoxy coatings are different animals, covering roughly 225 sq ft per gallon as a thin film. Add 10% for mixing losses and edge run-off.

The waste allowance

The calculator adds 10% for mixing losses and edge run-off, which is a modest allowance and deliberately so. Two-part epoxy is not like paint: once resin and hardener are combined the clock starts, the pot life is fixed, and whatever is left when it gels is refuse. You cannot decant half a kit and save the rest, so the practical unit of purchase is the kit rather than the gallon, and the useful question is how many kits rather than how many spare quarts. The larger risk on a floor is not running 10% short on material. It is preparing the slab badly, in which case the coating fails whatever quantity you bought. Budget the contingency in time and preparation, not just in resin.

Why a gallon of epoxy covers so much less than a gallon of paint

This surprises people, and it should not, because it is arithmetic rather than mystery. The Rust-Oleum data sheet for its water-based EpoxyShield floor coating gives a theoretical coverage of 844 to 847 square feet per gallon at 1 mil dry film thickness. That is the paper-thin number: what a gallon would cover if you could spread it one thousandth of an inch thick and it stayed there.

Nobody applies a floor coating at 1 mil. The recommended dry film thickness for that product is 3.0 to 3.5 mils, and the real published figure at that thickness is about 250 square feet per kit. Multiply the film thickness by three and a half and the area a fixed volume covers drops by the same factor. There is nothing else going on.

Solids content is the other half of the explanation. A coating is pigment and binder carried in a solvent or in water. The carrier leaves; the solids stay and become the film. A high-solids product leaves more behind per gallon applied, so it is applied wet at a lower spread rate to reach a much thicker dry film. Interior wall paint is built to leave about a mil of dry film and to stretch. A floor coating is built to leave three or more and to take abrasion, hot tyres and dropped tools. The same gallon simply cannot do both jobs.

The slab has to be ready before the kit is opened

New concrete needs a minimum of 28 days to cure before it is coated. This is the same 28 day figure used for concrete strength, and the reason overlaps: the slab is still hydrating and still giving off moisture, and a coating applied over it traps what has not yet left.

The surface then has to be etched, either with acid or mechanically, to give the coating something to grip. A smooth trowel-finished slab is the classic failure case. It looks like the ideal surface to coat, which is exactly the problem, because a burnished surface is closed and offers almost no mechanical key. Epoxy laid over it will delaminate, often in sheets, and usually after it has been in service long enough to feel like a success.

Mechanical profiling with a grinder or a shot blaster is more reliable than acid etching, mostly because it is harder to do inadequately. Acid etching works when it is done thoroughly and rinsed properly, and fails quietly when it is not. Either way the test is the same: a properly profiled slab feels like medium-grit sandpaper and takes a drop of water rather than beading it.

Moisture is what actually kills epoxy floors

The single most common cause of epoxy floor failure is moisture vapour moving up through the slab, and it is also the step most routinely skipped. Concrete on grade sits above damp ground. Water vapour travels through it continuously, and while the floor is uncoated that vapour simply leaves. Put an impermeable film over the top and the vapour arrives at a barrier instead, where it builds pressure under the coating and lifts it. The result is blistering and delamination, sometimes months after the job looked finished.

There are two standards worth knowing. ASTM F2170 is the in-situ relative humidity test, in which probes are placed in holes drilled into the slab and left to equilibrate, measuring the moisture condition inside the concrete rather than at its face. ASTM F710 is the standard practice for preparing concrete floors to receive resilient flooring and coatings, and it covers the condition the substrate needs to be in before anything goes down.

The reason this gets skipped is that it costs time and tells you nothing you want to hear. A slab that fails a moisture test does not stop being a slab you wanted to coat. But it is far cheaper to find out before the kits are opened than to grind a failed coating off afterwards, which is genuinely miserable work.

Conditions on the day, and how many coats

Surface temperature must be at least 5°F above the dew point. Below that margin, moisture condenses on the slab as you are coating it or shortly after, and the finish blushes and cures poorly. This catches people in garages in spring and autumn, when a concrete slab holds overnight cold well into a mild afternoon and sits below the dew point of the warmer air around it. Measure the slab, not the air.

Coat count is very product-dependent and it is worth reading your own kit rather than a general rule. The Rust-Oleum water-based product referenced here states that one coat suffices. Many other two-part systems require a base coat and a separate topcoat, and some add a clear coat over decorative flake. Those are different products with different film build targets, and their coverage figures are per coat.

This matters for buying, because a system needing two coats needs roughly twice the material for the same floor. Work out the coverage per coat, the number of coats the manufacturer specifies, and only then the number of kits. Guessing from a headline coverage figure without checking the coat count is how a two-car garage ends up half finished.

Floor coating figures and prerequisites

Coverage figures are from the Rust-Oleum water-based EpoxyShield data sheet. The preparation items are conditions the coating depends on, not optional refinements.

Coverage, film thickness and application conditions from the Rust-Oleum EpoxyShield water-based floor coating data sheet. Moisture test methods are ASTM F2170 and ASTM F710.

What goes wrong on garage floor coatings

Coating green concrete. New slabs need a minimum of 28 days before a coating goes on. Earlier than that the concrete is still releasing moisture into the underside of the film.

Skipping the moisture test. Vapour moving up through a slab is the most common cause of epoxy floor failure, and the test that catches it is the one most often left out. ASTM F2170 measures conditions inside the slab; ASTM F710 covers substrate preparation.

Coating a smooth trowel-finished slab as-is. A burnished surface gives the coating nothing to grip. Acid etching or mechanical profiling is what creates adhesion, and without it the film delaminates.

Ignoring the dew point. The slab surface must be at least 5°F above the dew point. Concrete holds overnight cold and can sit below it well into a mild afternoon.

Assuming one coat because one product says so. The Rust-Oleum water-based product states one coat suffices. Many two-part systems need a base coat plus a topcoat, which roughly doubles the material for the same floor.

Frequently asked questions

Why your state changes the price (but not the quantity)

How much epoxy you need is physics — it doesn't care where you live. What it costs does. Labor rates, delivery distance, fuel, and local demand move installed prices by roughly 45 points from end to end: Arkansas, Mississippi, North Carolina sit near the bottom of the range, while Alaska, Hawaii, New York sit at the top. The Price this for selector at the top of the calculator applies a published construction cost index for your state to the 2026 national averages, so the dollar figures move and the material list stays put.

Treat the result as a budgeting range, not a quote. Two metros inside the same state can differ by more than the statewide index suggests, and a single busy contractor can outweigh both. See the full cost index for all 50 states and where the price data comes from.