Epoxy Floor Calculator
Find out how many epoxy kits — or gallons — you need to coat a garage or basement floor.
Floor dimensions
Results
For a 22 ft × 20 ft floor coated with 1 coat, you'll need 2 kits at your kit's stated coverage — about 2.2 gallons of coating if buying by volume instead.
Epoxy kits needed
2 kits
That's a typical 2-car garage or mid-size basement floor.
Buy all kits at once and confirm matching batch numbers — epoxy color and gloss can vary subtly between production lots, and a visible seam mid-floor is permanent. Plan the pour so each mixed kit finishes at a natural break line, not mid-slab.
Floor area: 440 sq ft
By volume instead of kits: 2.20 gallons
How this works
The calculator multiplies your floor's length by its width to get the slab area, multiplies by the number of coats to get total coated area, and divides by two coverage figures in parallel: your kit's stated coverage (defaulting to 250 sq ft, the spec for a standard 1-car garage kit) to produce the primary whole-kit count, and a per-gallon spread rate (defaulting to a conservative 200 sq ft/gallon) to produce the by-volume secondary figure for products sold by the gallon rather than kitted. Kits are always rounded up to whole kits — partial kits can't be bought, and mixed epoxy can't be saved past its pot life. Both coverage figures are deliberately editable because they are properties of your product and your slab, not constants: manufacturer technical data sheets state coverage for smooth, properly prepped concrete, and porous or profiled surfaces cover meaningfully less, so the right workflow is to read your product's TDS, judge your slab's condition, and adjust the fields to match. The model assumes a rectangular floor — subtract permanent built-in footprints manually, and split L-shaped spaces into rectangles summed per run. What the calculator deliberately doesn't model is the workflow that epoxy demands and paint doesn't: surface prep, the moisture test, pot life, and cure schedule — covered in the sections above, because getting the quantity right is the easy half of an epoxy floor. The unit toggle switches every input and result between imperial and metric; internally all math runs in canonical units, so switching never introduces rounding drift Kit coverage (up to 250 sq ft per 1-car kit): Rust-Oleum EpoxyShield product specification.
Worked example
A 22 ft × 20 ft two-car garage, one coat, using kits rated at 250 sq ft: the floor area is 440 sq ft, so 440 ÷ 250 = 1.76 kits — rounded up to 2 kits, since epoxy is bought in whole kits. Buying by the gallon instead, at the default 200 sq ft/gallon rate: 440 ÷ 200 = 2.2 gallons raw. Note how close 1.76 sits to the 2-kit boundary: on smooth sealed concrete two kits is comfortable, but if this slab were bare and porous, effective coverage could drop toward 200 sq ft/kit and the same floor would genuinely need a third kit — the common-mistakes section's boundary rule applies.
A second example: a basement floor in two coats
A 30 ft × 15 ft basement (450 sq ft) coated with two coats for extra film build over porous older concrete, using the same 250 sq ft kits: the coated area is 450 × 2 = 900 sq ft, so 900 ÷ 250 = 3.6 — rounded up to 4 kits. By volume at 200 sq ft/gallon that's 4.5 gallons. Two things this example shows: coats multiply cost as directly as area does (this modest basement needs twice the material of the larger garage above), and a below-grade floor makes the moisture test non-negotiable before any of those four kits are opened.
Common mistakes
Trusting the kit's headline coverage on porous concrete
The '250 sq ft' on the box is a smooth-surface, ideal-conditions figure. Etched, broom-finished, or bare aged concrete routinely absorbs enough of the first coat to cut real coverage 20–30%. A 440 sq ft garage that 'should' take two kits can genuinely need a third on thirsty concrete — and running out mid-floor with mixed epoxy curing in the bucket is the worst possible place to discover it. Reduce the coverage figure to match your slab's condition before buying.
Skipping surface prep to save a weekend
Epoxy fails from below, not above. Oil spots, curing compounds, old sealers, and smooth steel-troweled surfaces all prevent the mechanical bond epoxy needs — the standard prep is degreasing plus acid etching or mechanical grinding until the slab feels like fine sandpaper and water soaks in rather than beading. Every manufacturer's warranty language starts with prep; nearly every peeling epoxy floor started with skipping it.
Ignoring the moisture test because the floor looks dry
Moisture vapor moving up through a slab is invisible until the coating traps it. The 24-hour taped-plastic test (or a calcium chloride test for rigor) is cheap and decisive: condensation under the plastic means stop — no standard epoxy will stay bonded. Coating anyway wastes the entire material budget this calculator just estimated, plus the far larger cost of grinding a failed coating back off.
Mixing all the kits at once for a big floor
Pot life makes mixed epoxy a countdown timer, and a double batch in one bucket cures faster (the reaction is exothermic — more mass, more heat, shorter working time). Mix one kit, roll it out to a planned break line, then mix the next. Working solo on a large floor, this is also self-protective: an over-ambitious mixed batch forces rushed application, and rushed epoxy shows every lap mark and thin spot permanently.
Coating outside the temperature and humidity window
Typical application windows are roughly 55–90°F with concrete above the dew point. Too cold and cure stalls (tacky floor for days, weak final cure); too hot and pot life collapses mid-roll. Slab temperature matters more than air — a garage slab in early spring can be 15 degrees colder than the air above it. Check the TDS window and put a thermometer on the concrete, not the wall.
Buying exactly the computed kits with no session buffer
The calculator rounds up to whole kits, which builds in some margin — but the margin shrinks to nothing when a floor's real coverage lands near a kit boundary. If your result is, say, 2 kits at 1.98 raw, one patch of porous slab tips you into a third kit mid-job. When the raw figure sits within about 10% of the boundary, buy the extra kit; unopened kits are returnable, half-coated floors are not.
Treating epoxy quantity like paint quantity
Paint forgives: you can stop anywhere, reseal the can, and resume next weekend. Epoxy commits: mixed material must be used within pot life, coats have recoat windows (too late and you must sand for adhesion), and cure milestones dictate when the space is usable. Plan the whole job — prep day, coat day, cure days — before opening anything, with the kit count from this calculator as the shopping list, not the schedule.
When this calculator's model stops applying
- 100%-solids and high-build commercial epoxies: these are specified by dry film thickness (mils), not sq ft per gallon in the retail sense — coverage is film-build math (a gallon covers 1,604 sq ft at exactly 1 mil, divided by your target mils). Use the manufacturer's mil spec, entering the resulting sq ft/gallon in the advanced field only as a cross-check.
- Full-broadcast flake or quartz systems: base coat, saturation broadcast, scrape, and one or two grout/top coats — total liquid volume is a system specification, often 2–3× a single-coat estimate, and each layer has its own spread rate.
- Vertical surfaces and stem walls: rolling epoxy up a curb or wall foot consumes material at a different rate than flat floors and usually needs a thickened or multiple thin passes; measure vertical faces separately and expect lower effective coverage.
- Heavily cracked, spalled, or out-of-level slabs: patching and self-leveling underlayment come first, and repair products have their own volume math (depth × area, like concrete). Coating quantity only makes sense after the substrate is a plane.
- Slabs with active moisture transmission (failed plastic-sheet test): standard epoxy should not be applied at all — moisture-mitigation primers or breathable coatings are a different product category with their own coverage specs.
- Countertops, tabletops, and casting resins: 'epoxy' there means self-leveling flood coats and deep-pour casting resins, measured in volume per area at specific pour depths (often quoted in oz per sq ft) — an entirely different calculation despite the shared chemistry.
- Exterior slabs in full sun: most epoxies amber and chalk under UV; exterior work uses polyaspartic or urethane systems whose spread rates differ. The area math holds, the product and its coverage figure don't.
- Freezers, coolers, and slabs below about 50°F at application: standard cure chemistry effectively stops; low-temperature formulations exist with their own coverage and film specs.
FAQ
How much epoxy do I need for a 2-car garage?
A typical 2-car garage runs 400–480 sq ft (about 20 × 22 ft). At the common 250 sq ft per kit spec — Rust-Oleum EpoxyShield's stated coverage for its 1-car kit — that's two 1-car kits for a single coat, or one 2-car/2.5-car kit rated at up to 500 sq ft. Enter your actual floor dimensions above; garages vary more than the '1-car/2-car' labels suggest, and a deep or wide bay can push you over a kit boundary.
How far does a gallon of epoxy go?
Water-based garage floor epoxies like EpoxyShield are specified around 200–250 sq ft per gallon per coat on smooth concrete — this calculator defaults to the conservative 200. High-build and 100%-solids epoxies are a different regime entirely: they're specified by film thickness (e.g., 100 sq ft per gallon at 16 mils), so a gallon covers far less area, deliberately. Always work from your specific product's technical data sheet, and use the adjustable coverage field to match it.
Why does rough or porous concrete need more epoxy?
Stated kit coverage assumes smooth, sealed-profile concrete. Porous concrete drinks the first coat: broom-finished, acid-etched, or shot-blasted surfaces have far more real surface area and open capillaries than their footprint suggests, and coverage can drop by a quarter or more. If your slab is rough, older, or was aggressively profiled during prep, reduce the kit coverage figure in the calculator rather than hoping the label number holds.
Do I need one coat or two?
Retail garage kits are formulated as one-coat systems, and one coat is the label instruction for a standard garage. A second coat makes sense over very porous concrete where the first coat soaked in unevenly, in commercial-use spaces, or when you want extra film build under a clear topcoat. The calculator's coats selector simply doubles the coated area — note that two coats means buying two rounds of kits, not stretching one kit thinner.
Does the calculator include primer or topcoat?
No — it estimates the color/base epoxy coat only. Some systems add a separate clear urethane or epoxy topcoat for gloss and abrasion resistance, and some manufacturers offer a primer for bare or patched concrete; both have their own coverage specs (clear topcoats often spread further than the base coat). Run this calculator once per product with each product's own coverage figure — the area and coat logic is identical.
What is pot life, and why does it change how much I buy?
Once the resin and hardener are mixed, the reaction starts and you typically have 1–2 hours of workable time (less in heat) before the batch stiffens in the bucket. You can't mix half a kit, pause a week, and mix the rest of that same batch after it's combined — which is why quantity planning matters more with epoxy than paint: each kit is a committed, single-session unit of work. Plan sections so each mixed kit finishes at a natural break line.
Do decorative flakes change the epoxy quantity?
Broadcast vinyl flakes don't consume extra epoxy — they're scattered onto the wet coat that's already down and the kits include them. What changes quantity is a full-broadcast (100% coverage) flake floor: those systems use a base coat, a heavier flake load, and then one or two clear coats to lock the flake in, roughly doubling or tripling total liquid volume versus a light-broadcast kit floor. Full-broadcast systems are usually bought as a system spec, not by this single-coat model.
Why is my concrete's moisture a bigger deal than the quantity?
Epoxy is vapor-tight; concrete with active moisture transmission pushes the coating off from below, and the failure (bubbling, hot-tire peeling) appears months later. Manufacturer instructions include a moisture test — commonly taping a plastic sheet down for 24 hours and checking for condensation — before any epoxy is opened. No quantity calculation saves a floor that fails the moisture test; slabs with vapor issues need a moisture-mitigating primer or a breathable coating instead.
How long before I can walk and park on the floor?
Typical water-based garage epoxy allows foot traffic after about 24 hours, but vehicle traffic needs a full cure — commonly 3 days minimum, and manufacturers often say up to 7 for full chemical/hot-tire resistance, longer in cool temperatures. This affects your plan more than your quantity: the car lives outside for most of a week, so schedule the job around weather and need for the space.
Should I subtract areas covered by cabinets or a workbench?
Only if they're permanent and sit directly on the slab. Coating under movable items is worth the small extra epoxy — layouts change, and an uncoated rectangle in the middle of a floor is permanent. For a large built-in you'll never move, measure its footprint and subtract it from the length × width area you enter, the same way the paint calculator handles doors and windows — just manually.
Can I use this calculator for basement floors or workshops?
Yes — the math is identical for any interior concrete slab: area × coats ÷ coverage. Two basement-specific cautions: below-grade slabs fail the moisture test more often than garages, so test first; and check that your product is rated for the space (some garage formulations specify ventilation requirements that a closed basement doesn't meet — water-based products are generally the basement-appropriate choice).
Can I switch between imperial and metric partway through?
Yes — the unit toggle converts every field you've already entered, including the kit coverage and per-gallon rate, so you won't lose your inputs. Internally the tool always computes from the same canonical values regardless of which unit is displayed, so switching back and forth doesn't introduce rounding error into the result.