Deck Stain Calculator

Measure your deck's length and width in feet and enter them, then pick how many coats you plan to apply — two coats is the standard for a durable, even finish. The calculator multiplies length × width to get your floor area, divides by a coverage rate (175 sq ft per gallon by default), multiplies by the number of coats, and rounds up to whole gallons so you never run short mid-project. Open More options to add railings and stairs, switch to metric, set your stain's exact coverage rate from the label, or enter a price per gallon for a quick cost estimate.

A gallon of deck stain covers a lot less than a gallon of wall paint. Most deck stains are rated for 150–300 sq ft per gallon, but bare, thirsty softwood like pine or cedar soaks up far more than a previously sealed or hardwood deck. That's why a safe default of 175 sq ft per gallon is used here — it leaves a little margin so you don't drive back to the store. Two coats are normal: the first coat seals and primes the wood, and the second evens out the color and adds protection. Because stain is sold only in whole gallons (and quarts), the final number is always rounded up. Measuring railings and stairs matters too — they can add 20–40% more surface area than the deck floor alone.

Gallons = (Deck area × Number of coats) ÷ Coverage rate, rounded up to the next whole gallon.

Deck area is length × width in square feet. Coverage rate is how many square feet one gallon covers — 175 sq ft/gal is a safe default for a semi-transparent stain on bare wood, though product labels range from 150 to 300 sq ft/gal. When you add railings or stairs, their surface area is added to the floor area before dividing, so the gallon count already includes them.

A 12×12 deck, 2 coats: 144 sq ft × 2 = 288 sq ft ÷ 175 = 1.65 gal → buy 2 gallons.

A 16×20 deck, 2 coats: 320 sq ft × 2 = 640 ÷ 175 = 3.66 → buy 4 gallons.

A 200 sq ft deck, 1 coat: 200 ÷ 175 = 1.14 → buy 2 gallons, because stain comes in whole gallons and you always round up.

- Always round up. Running out halfway leaves a visible lap mark where the wet edge dried.
- Match the label. If your stain lists a coverage rate (often 150–300 sq ft/gal), enter it under More options for a tighter estimate.
- Bare softwood drinks more. For new pine, cedar, or rough-sawn boards, add 10–15% to your total.
- Two thin coats beat one thick coat — they dry evenly and last longer.
- Buy the same lot. Purchase all your gallons at once so the color matches across cans.
- Keep a little extra for touch-ups after the first season.