Proper Estimate

Deck stain calculator

Enter the deck size, the railing and the stairs. With the coverage from your stain can, you get the gallons to buy for one or two coats.

Deck

Railing and stairs

0 if there's no railing

0 if there are no stairs

Stain

From the can. Most stains cover 150 to 300 sq ft per gallon.

Coats

Gallons to buy

4

for 2 coats

  • Deck floor192 sq ft
  • Railing144 sq ft
  • Stairs31 sq ft
  • Area to stain367 sq ft
  • Stain needed3.67 gal
  • Buy4 one-gallon cans

Railing counts as about 4 sq ft per foot, and each step as a tread plus a riser.

How the stain estimate works

The calculator adds up three areas, multiplies by the coats, and divides by the coverage per gallon:

  • Deck floor: length × width.
  • Railing: about 4 sq ft for every foot of railing, counting the posts, rails and balusters on all sides.
  • Stairs: each step is an 11 1/4 in tread plus a 7 1/2 in riser, about 1.56 sq ft for every foot of stair width.

It rounds up to whole gallons, and suggests five-gallon pails where they make sense.

Stain for common deck sizes

Deck size Floor area 1 coat 2 coats
10 × 10 ft 100 sq ft 1 gal 1 gal
12 × 12 ft 144 sq ft 1 gal 2 gal
16 × 12 ft 192 sq ft 1 gal 2 gal
16 × 16 ft 256 sq ft 2 gal 3 gal
20 × 16 ft 320 sq ft 2 gal 4 gal
20 × 20 ft 400 sq ft 2 gal 4 gal

Floor only, at 200 sq ft per gallon. Railings and stairs add more.

Coverage changes with the wood

Rough, weathered and new pressure-treated wood soaks up more stain than smooth or previously stained wood, so a first coat on old boards can cover far less than the can says. Second coats go further than first coats. Buy enough from the same batch so the color matches, and try it on a hidden spot first.

Before you stain

  • Clean the deck and let it dry completely.
  • Let new pressure-treated wood dry out: if water beads on it, wait; if it soaks in, it's ready.
  • Check the forecast. The can lists the temperatures and dry time the stain needs.

Questions

How much stain do I need for a 12 × 12 deck?

The floor is 144 sq ft, so at 200 sq ft per gallon that's 0.72 gallons a coat: one gallon for one coat, two for two. Railings and stairs add more; enter them above.

How much stain for a 16 × 12 deck with a railing?

With 36 ft of railing and five 4 ft steps, there's about 367 sq ft to stain. Two coats at 200 sq ft per gallon come to 3.67 gallons, so buy 4.

One coat or two?

Follow the directions on the can. Many stains call for two thin coats, and some are made to go on in one. Two thin coats last longer than one heavy coat, which can peel.

How long should new pressure-treated wood dry before staining?

Until it soaks up water. Sprinkle some on the boards: if it beads, wait; if it soaks in within a few minutes, the wood is ready. That can take a few weeks to a few months, depending on the weather.