Deck Stain Calculator

How to use this deck stain calculator

1. Measure the length and width of the deck floor and enter them with your unit.
2. If you will stain the railing, tick the railing box and enter the total length and the height. For stairs, enter the number of steps, the width, the tread depth and the riser height in the same unit.
3. Choose the number of coats and the coverage on your product's label. If you do not know it, pick the wood condition: smooth new wood soaks up less than rough or weathered wood.
4. Add a waste allowance and, if you like, a price per gallon to get a cost.

How do I calculate how much deck stain I need?

Gallons = total area × coats ÷ coverage per gallon. Total area is the deck floor plus the railings plus the stairs. For a 12 ft × 12 ft deck that is 144 square feet. Two coats at 200 square feet per gallon is 1.44 gallons. Add 10% for waste and you need 1.58 gallons, so buy 2 gallons.

How do I measure the railing and stairs?

For railing, multiply the total length by the height. Both faces are usually stained, so the calculator doubles it unless you untick the option. The spindles and the top rail are rough surfaces, so allow a little extra. For stairs, each step has a tread you walk on and a riser face. Area = steps × width × (tread depth + riser height).

Stain needed by deck size

Gallons for one and two coats at 200 sq ft per gallon with 10% waste, floor only:

Deck size	Area (sq ft)	1 coat (gal)	2 coats (gal)	Buy for 2 coats
10 × 10 ft	100	0.55	1.10	2 gal
12 × 12 ft	144	0.79	1.58	2 gal
12 × 16 ft	192	1.06	2.11	3 gal
16 × 16 ft	256	1.41	2.82	3 gal
16 × 20 ft	320	1.76	3.52	4 gal
20 × 20 ft	400	2.20	4.40	5 gal

Deck stain coverage per gallon

Typical coverage is between 150 and 300 square feet per gallon for one coat. The label on the can is the best guide.

Wood condition	Coverage (sq ft per gallon)
Rough, weathered or old wood	150 or less
Typical wood	200
Smooth or new wood	250 to 300

Another example: a 16 × 20 ft deck with railing and stairs

The floor is 320 sq ft. Railing 40 ft long and 3 ft high, both sides, adds 240 sq ft. Four steps 3 ft wide with a 0.9 ft tread and 0.6 ft riser add 18 sq ft. The total is 578 sq ft. One coat at 200 sq ft per gallon needs 2.89 gallons, and with 10% waste about 3.2 gallons, so buy 4 gallons. A common cost estimate for an average deck with railing and stairs is a few gallons, which matches this result.

Stain, sealer and the type of wood

• Semi-transparent stain shows the wood grain and is often applied in one coat.
• Solid stain hides the grain and behaves more like paint, often in two coats.
• Clear sealer protects with little color.
• Softwoods such as pine and cedar absorb more stain than dense hardwoods.

What changes the amount

Wood condition matters more than anything else. Old, rough or weathered boards can soak up far more stain than the best-case figure on the can, which is why the calculator offers a lower coverage setting. Railings, spindles and stairs are easy to forget and can add a third to the job. Spraying wastes more than brushing. Buy enough to finish in one batch if you can, since colour can vary slightly between cans, and follow the label on coats: some stains are meant to go on once only.