Gallons of stain = area × coats ÷ coverage per gallon. A 16 × 12 ft deck of smooth wood is 192 sq ft, 211 sq ft with 10% waste, and takes 1.2 gallons of Behr semi-transparent stain for its two required coats, so buy 2 gallons. The coverage depends on the stain and on whether the wood is smooth or rough.
How much stain to buy
gallons = area with waste ÷ coverage on the first coat + (coats − 1) × area ÷ coverage on later coats
Coverage is printed on the data sheet as a range in square feet per gallon, and it changes with the wood. The calculator buys against the spread rate for your wood: for rough or weathered wood, the sheet's rough rate when it has one and the low end of the printed range otherwise; for smooth wood, the sheet's smooth rate, or the midpoint of a single printed range. New, dry and rough wood soaks up more, so its numbers are lower. Add 10% waste for end grain, spindles and cutting in.
Stain coverage by product
Spread rates in square feet per gallon from the manufacturers' data:
| Stain | Type | Coverage | Coats |
|---|---|---|---|
| Cabot Australian Timber Oil (3400) | Transparent oil | 400 to 600 smooth, 250 to 350 rough | 1 only |
| Sherwin-Williams SuperDeck oil-based semi-transparent | Semi-transparent oil | 150 to 400 | 1 only |
| Behr Premium semi-transparent (5077) | Semi-transparent water-based | 250 to 300 first coat, 500 to 600 second | 2 |
| Thompson's WaterSeal semi-transparent | Semi-transparent water-based | 150 to 400 | 1 |
| Behr Premium solid color (5011) | Solid | 200 to 400 | not stated |
| Olympic Maximum solid | Solid, water-based | 250 to 350 | 2 |
Olympic says one gallon covers 250 to 350 sq ft depending on wood texture and porosity. Sherwin-Williams tells you not to apply more than one coat of its oil-based semi-transparent stain, and Cabot's sheet gives one coat, so the calculator holds those at 1.
Worked example: rough Behr semi-transparent, 400 sq ft
Behr's two required coats: the first at 250 sq ft per gallon, the second at 500. That is 400 ÷ 250 + 400 ÷ 500 = 1.6 + 0.8 = 2.4 gallons, so buy 3 gallons (one 1 gallon can and two more, or a 5 gallon pail if the price per gallon is lower). The same 400 sq ft with a one-coat product at 250 sq ft per gallon needs 1.6 gallons, two cans.
Transparent, semi-transparent and solid stain
Transparent stain shows the grain and has the least pigment, semi-transparent shows some grain and solid color covers the grain but shows the wood's texture, the way Olympic describes its solid stain. The type filter in the calculator lists the products in each group. Solid color usually needs two coats, and transparent stains often only one.
Wood stain for a fence, wall or deck
Pick the surface in the calculator: a deck is length × width; a fence is length × height, doubled for both sides; siding is length × height minus doors and windows. The fence and wall modes are flat areas only: for a deck with railings and stairs, use the deck stain calculator, which counts the balusters, rails and steps.
The next questions
- Painting instead? The exterior paint calculator and paint calculator work from the same area.
- Small pieces with a can? See the spray paint calculator.
- Need the area first? Use the square footage calculator.
- See every wall, ceiling and paint calculator.