Deck Stain Coverage Calculator
Find how many gallons of deck stain you need from the deck size, coats and the coverage rate, and estimate the total cost.
How it works
Area = L × W · Stained = area × coats · Gallons = ceil(stained ÷ coverage) · Cost = gallons × price
Deck stain coverage varies more than paint because bare, weathered and rough-sawn boards drink it up. Manufacturers quote 150–300 ft² per gallon, but the first coat on thirsty softwood lands at the low end. Calculate the flat surface area, multiply by coats, and divide by the tin’s rate — and remember that penetrating stains often specify a single coat, while film-forming ones want two. Add extra if you are also coating railings, balusters and stair stringers, which this surface-only figure leaves out.
Worked example
A 16 × 12 ft deck is 192 ft². Two coats means 384 ft² of coverage. At 200 ft² per gallon that is 384 ÷ 200 = 1.92 gallons, rounded up to 2 gallons — enough for the deck boards, though rails would need a little more.
Frequently asked questions
How many coats of stain does a deck need?
It depends on the product. Penetrating oil stains are usually one coat — a second just sits on top and can peel. Semi-transparent and solid film-forming stains often call for two. Always follow the label.
Why does the first coat use more stain?
Bare or previously stripped wood is porous and absorbs the first coat deeply, so coverage runs at the low end of the range. The second coat covers already-sealed wood and goes noticeably further.
Should I include the railings in the area?
This figure covers only the flat deck surface. Railings, balusters, fascia and stairs can add 20–50% more surface, so measure them separately or pad your gallon count if your deck has substantial railing.
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This calculator is for educational purposes. Double-check important results before acting on them.