Exterior wood

Deck stain calculator

How much stain for a deck? A 175 sq ft deck floor is about 1 gal of semi-transparent for one coat, 1 gal + 2 qt for two. Add the railing, spindles, and stairs and it grows: the 16 x 12 deck below lands at 2 gal + 1 qt. Semi-transparent covers around 250 sq ft a gallon, solid stain about 175.

Your deck

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Deck floor area—
Railing, spindles & stairs—
Total surface to coat—
Exact gallons needed—
CC-DECK · stain250 sq ft / gal / coat
Stain the deck when the boards are dry and the forecast is clear for a couple of days. A drop of water that beads means the old finish is still sealing; one that soaks in means the wood is ready. Overstaining a deck that cannot absorb leaves a sticky film that peels by August.

Buying stain and a pad applicator for the deck? Shop deck and fence stain on Amazon

How the math works

The floor is length times width: a 16 x 12 deck is 192 sq ft. Then the parts nobody measures. Railing runs about 1.5 sq ft per linear foot once you count the top rail, bottom rail, and post faces on both sides, so 40 ft of railing is 60 sq ft. Each baluster is about 1 sq ft of narrow faces, and a stair step (tread, riser, a bit of stringer) is about 3 sq ft. That default deck totals 291 sq ft of wood.

Coverage is where stain parts ways with paint. Semi-transparent covers about 250 sq ft per gallon, not the 350 a smooth wall gets, because rough deck boards drink it. The first coat on the 192 sq ft floor is 0.86 gallons after a 12% porosity buffer. The second coat is not a repeat: the wood is sealed now, so that coat reaches about 50% more area and needs only 0.51 gallons for the same floor. Add every coat for every part, round up to real cans, done.

Questions people ask

How much stain does a deck take?

A 175 sq ft deck floor is about 1 gal of semi-transparent stain for one coat, 1 gal + 2 qt for two. Add the railing, balusters, and stairs and a mid-size deck climbs fast: a 16 x 12 deck with a 40 ft railing works out to 2 gal + 1 qt at two coats. The rails and spindles carry more area than people expect.

Does a second coat of deck stain double the amount?

No, and this is the number most calculators get wrong. The first coat soaks into bare, thirsty wood; the second lands on sealed wood and lays on top, so it covers about 50% more ground per gallon. A second coat adds roughly two thirds of the first coat's paint, not another full pass. With some semi-transparent stains a second coat will not even absorb, so check the can.

Semi-transparent or solid stain, and how does it change the gallons?

Semi-transparent covers about 250 sq ft per gallon and lets the grain show; solid (opaque) covers about 175, roughly 30% less, and hides the wood like paint. Solid also usually wants two coats, so a solid-stain deck can take nearly double the semi-transparent number. Pick the look first, then read the gallons off the calculator.

Why plan for a porosity buffer?

Bare, weathered, or pressure-washed boards drink stain. We add a 12% allowance on the first coat so a fresh-sanded or sun-grayed deck does not leave you a board short at the far corner. Previously sealed wood in good shape uses less, so on a light refresh you can round down.

Related

Fencing off the yard too? Fence stain calculator (the other half of the outdoor-wood job). Painting the house body: exterior paint calculator. How far a gallon really goes: coverage per gallon. One coat or two: the coats guide.