How it works
The calculator works out the deck floor area, adds the railings, steps and other parts you enter, multiplies by the number of coats and divides by the stain’s coverage.
Deck floor = Length × Width
Area to stain = Deck floor + Railings, steps & other
Stain = Area to stain × Coats ÷ Coverage × (1 + Extra ÷ 100)
Cans = ⌈ Stain ÷ Can size ⌉
⌈ ⌉ means rounding up to the next whole number: you can’t buy part of a can. The stain volume itself is not rounded. In “known deck area” mode the area you enter replaces length × width.
For the worked example above, a 16 × 12 ft deck has a floor of 192 sq ft. With 60 sq ft of railings and steps the area to stain is 252 sq ft. Cabot Solid Color Oil Stain Low VOC lists 200–300 sq ft per gallon on rough surfaces, so at the low end of 200 sq ft per gallon one coat takes 252 ÷ 200 = 1.26 gallons – two one-gallon cans. On smooth, planed boards the same sheet gives 400–500 sq ft per gallon, and the deck needs 252 ÷ 400 = 0.63 gallons, which fits in one can.
Deck stains vary more in coverage than wall paints do. A penetrating transparent or semi-transparent stain soaks into the wood, and how much it soaks in depends on the species, how rough and how old the boards are and how dry they are on the day. The data sheets used here run from 100 to 500 sq ft per gallon. That is why the calculator has no generic “stain coverage” figure: pick your product to apply the rate from its manufacturer’s technical data sheet, or type the figure from your can. Where a sheet gives a range, the low end is used, so the estimate leans towards more stain. Where a sheet gives separate figures for rough and smooth wood, a “Wood surface” choice appears; it starts on rough, the more conservative choice.
The age of the wood matters as much as its texture. Sherwin-Williams’ SuperDeck sheet notes that new wood normally requires less product than old, weathered wood, because older wood is more porous. Tikkurila gives two ranges for Valtti Plus Terrace Oil – 5–7 m² per liter on old and worn wood and 7–15 on new wood in good condition – and the calculator uses the lower, old-wood figure. If your deck is new and smooth, you may well have stain left over; if it is gray and thirsty, an extra allowance is sensible.
The number of coats comes from the label, not from habit. Some products are designed for one coat – Cabot and Benjamin Moore note that extra coats can raise the sheen – while others need two coats for even color. The stain volume scales directly with the coats you enter.
Measurements, coverage and can size are converted to one internal unit before calculating, so you can enter the deck in feet and inches and pick gallons or quarts for the cans. One US gallon is 231 cubic inches (NIST Handbook 44) and equals four quarts. In metric, coverage is in m² per liter; can sizes vary by brand and market, so none is filled in – enter the size you’ll buy to see the number of cans. The coverage used is shown with the result, and the data sheets behind every product are linked under Sources.
Worked example
Inputs
- Measure by
- Deck length × width
- Deck length
- 16 ft
- Deck width
- 12 ft
- Railings, steps & other area
- 60 sq ft
- Number of coats
- 1
- Stain product
- Cabot Solid Color Oil Stain Low VOC – 200 sq ft/gal rough, 400 smooth (≈ 4.9 / 9.8 m²/L)
- Wood surface
- Rough (sawn or weathered)
- Extra stain
- 0 %
- Can size
- 1 gal
Result
- Deck floor
- 192 sq ft
- Railings, steps & other
- 60 sq ft
- Area to stain
- 252 sq ft
- Coverage used
- 200 sq ft/gal
- Stain needed
- 1.26 gal (5.04 qt)
- Cans
- 2
Common mistakes
- Measuring only the deck floor. Stair treads and risers, railings, balusters, posts and fascia can add a large share of the area – measure them and add it to the calculation.
- Using a smooth-wood coverage figure on rough or weathered boards. Rough-sawn and old, gray wood soaks up much more stain. For products with two figures, choose the rough surface if in doubt.
- Applying more coats than the label calls for. Some penetrating and solid stains are made for one coat and say a second coat can raise the sheen; others require two. Use the number on your data sheet.
- Buying exactly the calculated amount for a large deck. Tikkurila’s sheet advises reserving enough of the same batch to ensure a uniform surface, so buy enough for the whole job at once.
- Using a stain’s coverage on a different product. Spread rates between transparent, semi-transparent and solid stains differ by a factor of two or more.
Assumptions and limits
- The deck floor is a rectangle of length × width, or the area you enter. Gaps between boards are not subtracted, and board edges and ends are not added.
- Railings, steps, benches and other parts are included only through the area you enter. The calculator does not estimate them from the deck size.
- Coverage is the documented rate of the product you pick – the low end of the range on its data sheet – or the figure you type, and it applies to every coat. For a product with separate rough and smooth figures, the rough figure is used unless you choose smooth.
- Real coverage depends on the wood species, its age and condition, how porous it is, the weather and how the stain is applied.
- Cans are rounded up to whole containers of the size you choose; the calculator does not mix gallons and quarts.
Frequently asked questions
How many square feet does a gallon of deck stain cover?
It varies widely with the product and the wood. The data sheets used here list 100–350 sq ft per gallon for Sherwin-Williams SuperDeck Waterborne Semi-Transparent, 200–400 for Benjamin Moore Arborcoat Translucent, 300–400 for Arborcoat Semi Solid and Solid Color, and 400–500 on smooth and 200–300 on rough surfaces for Cabot Solid Color Oil Stain Low VOC. Tikkurila lists 5–7 m² per liter on old and worn wood for Valtti Plus Terrace Oil. The calculator uses the low end of each range.
Do I need one or two coats of deck stain?
Follow the label for your product. Cabot’s Solid Color Oil sheet recommends one coat and says two coats may result in a higher sheen, Tikkurila says to apply one coat of Valtti Plus, Benjamin Moore’s Arborcoat sheets give one or two coats depending on the product, and SuperDeck Waterborne Semi-Transparent requires two coats for proper color development.
How do I measure deck railings and stairs?
Treat each part as a rectangle. For stairs, add up each tread’s width × depth and each riser’s width × height. For railings, take the length × height of each section; for balusters and posts, add up their faces you’ll actually stain. Enter the total in “Railings, steps & other area”.
Why is rough wood different from smooth wood?
Rough-sawn and weathered surfaces soak up more stain. Cabot’s data sheet, for example, gives 400–500 sq ft per gallon on smooth surfaces but 200–300 on rough surfaces, so the same deck can need about twice as much stain if the boards are rough.
Can I use this for a clear sealer?
Yes, if you know its coverage. Choose “Your own coverage” and enter the spread rate from the sealer’s can or data sheet; the method is the same.
Sources
- Arborcoat Waterborne Exterior Stain Semi Solid (639) Technical Data Sheet — Benjamin Moore. Exterior wood stain: "Coverage per Gallon at Recommended Film Thickness 300 – 400 Sq. Ft." (preset uses 300).
- Arborcoat Waterborne Exterior Stain Solid Color (640) Technical Data Sheet — Benjamin Moore. Exterior wood stain: "Coverage per Gallon at Recommended Film Thickness 300 – 400 sq. ft." (preset uses 300).
- Arborcoat Waterborne Exterior Stain Translucent (623) Technical Data Sheet — Benjamin Moore. Deck and siding stain: "Coverage per Gallon at Recommended Film Thickness 200 – 400 sq. ft." (preset uses 200).
- Cabot Solid Color Oil Stain Low VOC (#7600 Series) Product Data Sheet — Cabot (Sherwin-Williams). Decks and railings: "On smooth surfaces approximately 400–500 sq. ft. (37–46 m2) per gallon. On rough surfaces, 200–300 sq. ft. (18–27 m2) per gallon." (presets use 400 smooth, 200 rough).
- SuperDeck Exterior Waterborne Semi-Transparent Stain (SD3T00025) Product Data Sheet — Sherwin-Williams. Deck stain: "Coverage: 100-350 sq. ft. per gallon" "Depending on porosity and texture." and "Two coats are required for proper color development" (preset uses 100).
- Valtti Plus Terrace Oil Product Data Sheet (19.06.2024) — Tikkurila. Terrace oil: "Old and worn wood surfaces 5–7 m²/l. New surfaces or wood surfaces in good condition 7–15 m²/l" and "Apply one coat." (preset uses 5).
- NIST Handbook 44, Appendix C – General Tables of Units of Measurement — National Institute of Standards and Technology. Exact unit definitions: 1 in = 2.54 cm, 1 yd³ = 27 ft³, 1 US gal = 231 in³, 1 lb = 0.45359237 kg.
Method reviewed November 3, 2026