Epoxy floor coating calculator

When you buy floor epoxy by the gallon, coverage depends on film thickness, measured in mils (thousandths of an inch). At 10 mils wet, a gallon covers about 160 sq ft; double the thickness and you halve the coverage. If the data sheet gives dry film (DFT), say so in the calculator and enter the volume solids; if it gives a coverage rate instead, enter that.

Mils, coverage and gallons

A mil is a thousandth of an inch. Floor coating data sheets usually give a recommended film thickness in mils (or microns) and a coverage rate at that thickness. The two are tied together by one number: a US gallon is 231 cubic inches, and spread 1 mil thick it covers about 1,604 sq ft (231 ÷ 0.001 ÷ 144). So coverage per gallon is simply 1,604 divided by the wet film thickness in mils. Spartan Epoxies’ layer chart lists its floor coating at about 133 sq ft per gallon at 12 mils and 267 sq ft at 6 mils, which is the same arithmetic. If your data sheet gives the coverage rate directly, switch Data sheet gives to coverage rate and enter it.

wet mils = dry mils ÷ volume solids (when the sheet gives DFT)
coverage (sq ft/gal) = 1,604 ÷ wet mils
gallons per coat = area × (1 + waste) ÷ coverage
metric: m² per liter = 1,000 ÷ wet film in µm

For a 30 × 20 ft basement (600 sq ft) at 10 mils: coverage is about 160 sq ft per gallon, so one coat needs 3.74 gallons, or about 4.3 gallons with 15% for porous concrete and roller losses. Two coats doubles that to roughly 8.6 gallons — three 3-gallon kits.

Worked examples at other sizes: How many gallons of floor epoxy for 400 sq ft at 10 mils (a 20 × 20 ft garage), How much epoxy for a 1,000 sq ft basement floor, and in metric, How much epoxy for a 50 m² floor.

Wet film vs dry film

A 100%-solids epoxy cures to about the thickness you roll on. Water-based and solvent-based coatings lose their water or solvent as they dry, so the cured film is thinner than the wet one. If the sheet gives DFT, gallons = area × DFT ÷ solids — a 50%-solids coating needs twice the gallons of a 100%-solids one for the same cured film. Set The data sheet’s film thickness is to Dry film (DFT) and the calculator does the division: 3 mils DFT at 50% solids is 6 mils wet, so two coats on 600 sq ft take about 5.16 gallons with 15% waste, not the 2.6 you’d get by treating 3 mils as wet film.

Primer, base coats and topcoat

Most pro floor systems are more than one product: a thin primer that soaks into the concrete, one or more base coats, and often a clear topcoat — for example over a flake broadcast. Each is its own purchase, so the calculator works out gallons and whole kits for each separately rather than pooling them.

• Primer goes by the coverage rate on its data sheet. ArmorPoxy, for example, lists its epoxy primer at about 220–320 sq ft per gallon at 5–7 mils. Bare, freshly ground concrete drinks primer, so the calculator adds 20% by default — raise it for very porous slabs.
• Base coats use the film thickness (wet or dry) and the number of coats above.
• Topcoat has its own thickness and volume solids. Over flakes the surface is rough, so the calculator multiplies the topcoat by 1.2 for a partial broadcast or 1.5 for a full one. Those are planning allowances, not a maker’s figure — if your flake system’s data sheet gives a topcoat rate over chips, use it.
• Cove base — coating carried up the wall as a curved skirting, usually 4 or 6 in high — adds its wall area to the base and topcoat (and the primer).

Sections, batches and film thickness

With a kit size entered, the calculator also shows how much floor one batch should cover: batch volume ÷ (1 + waste) × coverage. A 3-gallon kit at 10 mils with 15% waste covers about 418 sq ft. Chalk-line the floor into sections that size before you mix. It’s the easiest way to hit the target thickness without a wet-film gauge — if a batch runs out early, you’re going on too thick; if there’s coating left at the line, you’re going on thin. Mixing half kits instead? Enter the batch size under Largest batch you’ll mix.

Why concrete eats more than the math says

• Bare, ground or etched concrete absorbs the first coat. Primers exist partly for this reason.
• Rough surfaces have more real surface area than their footprint.
• Rollers, trays and the bottom of the bucket all hold material you never get back.
• Leave the allowance at 15% for most floors, and raise it for very porous or badly worn concrete.

Pricing the floor for a client? The floor job bid calculator takes the same primer, base and topcoat quantities, adds flake boxes and labor hours per step, then your prices and markup.

Ventilate while the coating goes down and cures: the EPA recommends increasing ventilation when using products that emit volatile organic compounds, and solvent-based coatings emit a lot of them.