Concrete sealer calculator

How many gallons of sealer a slab takes depends on two things most calculators ignore: whether the sealer soaks in or films over, and how rough the surface is. Set both and get the real number.

01 How the math works

The volume of sealer is area times coats divided by the coverage rate, rounded up to the whole gallon. The only hard part is the coverage rate, and that is where sealers differ from paint.

A penetrating sealer — silane or siloxane — soaks into the slab and leaves no film. Its coverage is set by how much the concrete absorbs, so it runs 150–400 ft²/gal across the porosity range: dense, power-troweled concrete reaches 400 ft²/gal, open or porous concrete drinks it down to 150 ft²/gal, and a standard broom finish sits near 250 ft²/gal.

A film-forming acrylic — a cure-and-seal or decorative topcoat — lays a thin film on top, so its coverage is a per-coat film rate like paint. A water-based acrylic at 20% solids covers 150–200 ft²/gal per coat, again depending on texture. One flat "ft²/gal" number can't describe both, which is the whole reason this calculator asks for the type first.

02 Worked example

Take a 20 ft × 40 ft broom-finished driveway (6.10 m × 12.19 m) — 800 ft² (74.32 m²) — getting two coats.

With a penetrating sealer at the broom rate of 250 ft²/gal (6.14 m²/L): 800 ÷ 250 × 2 = 6.4 gal (24.2 L), order 7 gallons.

With a water-based acrylic cure & seal at the broom rate of 175 ft²/gal (4.29 m²/L): 800 ÷ 175 × 2 = 9.14 gal (34.6 L), order 10 gallons — two 5-gallon pails.

Same slab, same two coats, but the acrylic order runs about 43% higher, because the film sealer lays a thin coat on top while the penetrating sealer soaks into the slab. Switch the type on the calculator above and watch the gallon count move — the area never changed.

03 When this calculator is wrong

Coverage figures on a sealer can are measured on clean, cured, dry concrete at the manufacturer's reference conditions. The number moves with the slab in front of you.

• Surface texture is porosity, and porosity is coverage. Rough, broom-finished, or stamped concrete absorbs roughly 20–40% more sealer than smooth hard-troweled concrete — about a 25% cut to the smooth-surface rate. On the 800 ft² driveway above, that's the difference between ordering 6 and 8 gallons. Pick the finish that matches the pour, not the one that orders less.
• A second penetrating coat takes the same as the first. Penetrating coats go on wet-on-wet into still-open pores, so the second coat is not thinner. The AM 21 data sheet lists one coat at 150–400 ft²/gal and two coats at 75–200 — exactly half, meaning two coats use 2× the sealer. Do not plan a penetrating second coat the way you would a second coat of paint.
• A fresh pour isn't ready to seal. Most sealers want concrete cured 28 days before a topical acrylic goes down (a cure-and-seal is the exception — it's meant for green concrete). Seal too early and a topical film can trap moisture in the slab — a curing problem, not a coverage one.
• Solvent-based acrylics cover further. The acrylic figures here are for a common water-based cure-and-seal. A thin solvent-based decorative acrylic covers more per coat — around 300 ft²/gal on smooth troweled and 200 ft²/gal on stamped over two coats. Read the can and override the finish if your product's number differs.

04 What to do with the result

Order the rounded-up number, and lean one increment high rather than low. The cost of a returned gallon is small; the cost of stopping a driveway halfway through a coat to drive for one more pail is a lap mark that shows for the life of the sealer. On this site the rule is always what to order, not what the math gives you — round up to the pail.

The exception is a tinted or solid-color sealer bought in a custom batch: like custom-mixed paint, those can be hard to match later, so buy the full job at once from a single batch rather than topping up mid-project. For clear sealer in standard 1-gallon cans and 5-gallon pails, a spare gallon on the shelf is cheap insurance.

05 Common questions

How much concrete sealer do I need for a driveway?

For a typical 800 ft² (74.32 m²) broom-finished driveway at two coats: about 7 gallons of a penetrating sealer (250 ft²/gal) or 10 gallons of a water-based acrylic (175 ft²/gal). Set your own dimensions and finish above — the gap between the two chemistries is real, not rounding.

How many coats of concrete sealer should I apply?

Two is standard for both families. Penetrating sealers take a second wet-on-wet pass to fully saturate the pores; acrylics get a second thin coat for an even film and more gloss. A single coat is a maintenance re-seal on an already-sealed surface, not a first-time job.

How much does a gallon of concrete sealer cover?

Per coat: a penetrating silane/siloxane covers 150–400 ft²/gal depending on porosity (about 250 on a broom finish), and a water-based acrylic covers 150–200 ft²/gal. The range is the surface texture — a smooth troweled slab lands at the high end, stamped or porous concrete at the low.

Does penetrating or acrylic sealer cover more per gallon?

On the same broom-finished slab, the penetrating sealer covers more ground per gallon (250 vs 175 ft²/gal here) because it soaks in rather than building a film. That doesn't make it cheaper overall — the two do different jobs. Penetrating sealers protect from within and keep a matte look; acrylics add sheen and surface protection but need re-coating sooner.