Concrete Sealer Coverage Calculator: How Many Gallons Do You Need?

Sealing a concrete slab is the difference between a surface that lasts and one that stains, spalls, and crumbles a few winters in. But buying the sealer is where DIYers get confused, because coverage rates vary wildly — from 150 to 400 square feet per gallon — depending on the sealer type and the porosity of the concrete. Here is how to calculate the gallons you need for your slab, in a straightforward formula you can apply to any project.

The Basic Coverage Formula

Every gallon of concrete sealer has a rated coverage, printed on the label, expressed in square feet per gallon. The math is simple:

Total Square Feet / Coverage per Gallon = Gallons Needed

Measure your slab's length and width in feet and multiply for the area. For a 10x10 patio, that is 100 square feet. Most penetrating and film-forming sealers rate between 200 and 400 square feet per gallon on smooth, non-porous concrete. At a typical 250 square feet per gallon, your 100-square-foot patio needs 100 / 250 = 0.4 gallons per coat — under half a gallon. Since sealer is sold in whole gallons and you need two coats, buy one gallon.

The Two-Coat Rule

Nearly every sealer requires two coats, and this is where people under-buy. The first coat soaks into the porous surface and mostly disappears; the second coat forms the durable film that repels water and stains. So the formula above gives you the gallons per coat, and you multiply by two for the total purchase. A 10x10 patio at 250 square feet per gallon needs 0.4 gallons per coat, or 0.8 gallons total — rounded up to one gallon. A full 2-car garage at, say, 20 x 20 = 400 square feet needs 400 / 250 = 1.6 gallons per coat, or 3.2 gallons total — so you buy 4 gallons to be safe.

Coverage Rates by Sealer Type

Not all sealers cover the same, and choosing the right type changes both the gallon count and the price. Here are the three main categories:

• Acrylic film sealers: 150 to 300 square feet per gallon. These form a glossy, wet-look film and are the most common for decorative patios and stamped concrete. Cheaper to buy but need reapplying every 1 to 3 years.
• Penetrating sealers: 200 to 400 square feet per gallon. These soak into the surface and repel water without changing the look. Ideal for driveways and sidewalks where you do not want gloss. Longer-lasting, applied once.
• Epoxy and urethane coatings: 150 to 250 square feet per gallon, but these are heavy-duty floor coatings that usually go on garage and shop floors. Pricier per gallon and best left to professionals.

A common trap is assuming the higher coverage rate on the label. The 400-square-foot figure assumes perfectly smooth, low-porosity, new concrete. Old, spalled, or rough concrete can soak up 50% more product. If your slab is porous or weathered, drop the rated coverage by a third and recompute — it is cheaper to buy a little extra than to run out mid-coat and have to feather a second batch over a partially sealed surface.

Worked Example: A 12x24 Stamped Patio

Let's cost out a 12x24 stamped patio, which is 288 square feet, using an acrylic sealer rated at 200 square feet per gallon (stamped surfaces are textured and absorb more). Per coat: 288 / 200 = 1.44 gallons. Two coats: 2.88 gallons, so buy 3 gallons. At roughly $25 to $40 per gallon for quality acrylic sealer, the material runs $75 to $120. If instead you use a penetrating sealer rated at 300 square feet per gallon, per coat is 288 / 300 = 0.96 gallons, and two coats need 1.92 gallons — buy 2 gallons at $30 to $50 each, or $60 to $100. The price difference is small, but the penetrating option lasts longer and keeps the stamped texture looking natural.

Whatever your slab size, measure carefully, use the rated coverage with a porosity haircut for older concrete, and always double the per-coat figure for the two-coat application. A single-coat job is the most common reason a sealed slab stains within a year.