Easy Epoxy Calc

How many gallons of floor epoxy for 400 sq ft at 10 mils?

Short answer

You need about 5.74 gallons of floor epoxy for two 10-mil coats on 400 square feet — 2.87 gallons per coat of a 100%-solids coating, including 15% for absorption and roller losses.

How to work it out

  1. 20 ft × 20 ft = 400 sq ft
  2. 1,604 ÷ 10 mils = 160.4 sq ft/gal
  3. 400 sq ft ÷ 160.4 sq ft/gal × 1.15 = 2.87 gal per coat × 2 = 5.74 gal
  4. 5.74 gal ÷ 3 gal per kit = 1.91 → 2 kits
  5. Area per batch = 3 gal ÷ 1.15 × 160.4 sq ft/gal = 418 sq ft of base coat

Four hundred square feet is a 20 × 20 ft two-car garage, and 10 mils (ten thousandths of an inch) wet is a common per-coat film for 100%-solids floor epoxy. Buying by the gallon is the route where you control the film thickness; boxed kits are rated in square feet instead.

Buying boxed kits rather than gallons? See How much epoxy for a 20×20 two-car garage for the kit count on the same floor.

Adjust for your project

ft
Wall to wall, in feet.
ft
Wall to wall, in feet.
Wet film (WFT) is what you roll on; dry film (DFT) is what’s left once the coating has cured. Most floor data sheets give DFT — check which yours says.
mils
From the data sheet (1 mil = 1/1,000 in). Thin water-based coats are around 4 mils, 100%-solids coats often 8–20.
Coats of this product. A clear topcoat of a different product goes in Topcoat below.
%
On the data sheet as “volume solids” or “solids by volume”. 100%-solids epoxy is 100; water-based coatings are much lower.
mils
A clear coat of a different product over the base — e.g. to lock in flakes. Same basis (wet or dry) as above. Leave blank for none.
sq ft/gal
Leave blank for no primer. From the primer’s data sheet — ground concrete: typically 200–300 sq ft/gal.
gal
Mixed size of one kit or pail — both parts together.
More options: cove · waste · batch …
ft
Cove base = the coating carried up the wall as a curved skirting. Enter the length of wall it runs along; leave blank for none.
%
Porous concrete, roller and tray losses
gal
Mixed coating per batch. Leave blank to mix one whole kit at a time — the usual way on floors.
$
Optional — your kit price, for a cost estimate (the same price is used for every product).
Floor coating to buy (all coats)5.74 gal22.9 qt · 21.7 L
Kits to buy
2 kits
Per base coat
2.87 gal (11.5 qt · 10.9 L)
Floor area
400 sq ft
Theoretical coverage per base coat
160.4 sq ft/gal
Wet film per base coat
10 mils
Approx. dry film per base coat
10 mils
Batches per base coat
1 batch
Area one batch covers
1 × 3 gal kit ≈ 418 sq ft at 10 mils — chalk-line the floor into sections this size
Left over in part-used kits
0.26 gal (1.06 qt · 1 L)
  • What to buy: 2 × 3 gal kits of floor coating. Each kit has both parts (resin + hardener) — you don’t buy them separately. Looking at a different kit size? Change Size of the kit you’re buying above.
  • Tight fit: only 0.26 gal spare. Thirsty or freshly ground concrete can use that up in the first coat — consider one more kit.

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Floor epoxy coating (by the gallon)Plan on 5.74 gal — 2 × 3 gal kits. Check that the data sheet’s coverage at 10 mils wet matches — that’s the number the gallons hang on.
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Gallons for 400 sq ft at 10 mils by number of coats (3 gal kits)

Gallons for 400 sq ft at 10 mils by number of coats (3 gal kits)
CoatsFloor coating to buy (all coats)Kits to buyLeft over in part-used kits
1 coat2.87 gal1 kit0.13 gal
2 coats5.74 gal2 kits0.26 gal
3 coats8.6 gal3 kits0.4 gal

What to know about coating 400 sq ft at 10 mils

At 10 mils a gallon covers about 160 sq ft in theory, so the bare film on 400 sq ft is 2.5 gallons a coat; the 15% allowance brings it to about 2.87. Two 3-gallon kits hold 6 gallons against 5.74 needed, leaving about a quarter of a gallon — under 5% spare. One kit is meant to cover about 418 sq ft at this film, so each coat is one kit with very little left in the bucket. On thirsty, freshly ground concrete that can vanish in the first coat, which is one reason many systems start with a thin primer.

You can use the same numbers to check what a boxed kit really assumes. Multiply the mixed gallons in the box by 1,604 and divide by its rated coverage: that’s the film in mils it expects. A kit holding 1 gallon of mixed coating and rated for 250 sq ft is planning on roughly 6.4 mils — thinner than the 10 mils here, which is why kit counts and gallon counts for the same garage rarely agree.

To hit 10 mils without a wet-film gauge, split the floor with tape into four 10 × 10 ft squares and give each one about a quarter of a coat’s material — roughly 0.7 gallons including the allowance. If a square runs dry early, you’re rolling too thick; if there’s coating left, you’re going on thin.

For a bigger floor at the same film, see How much epoxy for a 1,000 sq ft basement floor.

Different size? Use the full Epoxy Floor Coating Calculator.

What you’ll need

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Frequently asked questions

How many gallons of floor epoxy for 400 sq ft at 16 mils?

About 9.18 gallons for two coats — 4.59 gallons per coat, because coverage drops to 100.3 square feet per gallon at 16 mils.

How many 1-gallon kits for two coats on 400 sq ft at 10 mils?

6 kits: two coats need 5.74 gallons with the 15% allowance, leaving 0.26 gallons over.

How thick is a 50% solids coating on 400 sq ft at 10 mils wet?

It still takes 5.74 gallons for two coats, but each coat dries to only about 5 mils once the water or solvent has left.

How much 50% solids floor coating for 400 sq ft at 5 mils dry film?

About 5.74 gallons for two coats: 5 mils dry ÷ 50% solids is 10 mils wet, so it takes the same gallons as a 100%-solids coating rolled at 10 mils — twice what the dry figure alone suggests.

Other common sizes

Sources