Deck and Fence Stain Calculator
Find how much stain you need for a wood deck, its railings and stairs, or a wood fence. Enter the size of each surface, the wood surface, the coverage on the label, and the number of coats to see the gallons or liters of stain and how many cans to buy. It works for transparent, semi-transparent, semi-solid, and solid stains, clear water sealers, and decking stain or fence treatment.
Add railings, stairs, or a fence. For a railing or fence, enter its height as Width, and set Quantity to 2 to stain both sides.
- Choose US or Metric. You can still change the unit of any single field.
- The first section is a Rectangle. Enter the Length and Width of the deck floor. For an L-shaped deck, add a rectangle for each part.
- Use Add section for railings, stairs, or a fence. For a railing or a fence, enter its length as Length and its height as Width, and set Quantity to 2 to stain both sides. Set a section to Subtract for areas you won't stain, such as an opening for a hot tub.
- Choose the Wood surface. Pick Rough-sawn for boards that feel rough to the touch, or for old, weathered wood that soaks up water quickly.
- Check the Coverage per coat. It starts at a typical value for the wood surface. Enter the per-coat coverage on your stain's label.
- Enter the number of Coats on your label. It starts at 1 with US units and at 2 with Metric units.
- Check the Waste allowance. It starts at 10%. Optionally, enter a Custom can size and a price per can, gallon, or liter to estimate the cost.
For a round or curved deck, enter its area as a
Known area, or enter the rectangle around it, which
gives a little more stain than you need. Before you stain, clean the wood,
and strip or brighten it if your stain's label says to. The calculator
doesn't count cleaners, strippers, or brighteners. Dimension fields
accept whole numbers, decimals, fractions, and mixed numbers, such as
12, 12.5, 3/4, or
8 1/2.
How much deck stain you need
The calculator adds up the area to stain, adds the waste allowance, and multiplies by the number of coats before dividing by the coverage per coat:
Total area = net area × (1 + waste % ÷ 100)
Stain = total area × coats ÷ coverage per coat
Cans = stain ÷ can size, rounded up
With several sections, the calculator adds the sections set to Add and subtracts those set to Subtract. Each section's area is multiplied by its Quantity. The area of each shape is calculated as follows:
| Shape | Area |
|---|---|
| Rectangle | length × width |
| Known area | the area you enter |
Railings, stairs, and fences
Every part of a deck or fence can be entered as a rectangle. Measure in feet or meters and add one section for each part:
| Part | What to enter |
|---|---|
| Deck floor | Length × Width, Quantity 1 |
| Railing | Length × height (as Width), Quantity 2 for both sides |
| Fence | Length × height (as Width), Quantity 2 for both sides, or 1 for one side |
| Stairs | Stair width × (tread depth + riser height) as Width, Quantity = the number of steps |
Counting a railing or fence as a flat surface on both sides is an estimate. A fence side has gaps between boards but also posts and rails, and Cuprinol counts its fence treatment in fence panels of about 3 m² each, the same as length × height. On a railing with balusters, you stain all four sides of each baluster and the top and bottom rails, which comes close to length × height on both sides. For a 3 ft railing with 2×2 balusters spaced 3 1/2 in apart, the balusters alone take about 3.6 ft² per foot of railing. Treat the railing area as a guide, and keep the waste allowance.
Coverage and the wood surface
Coverage is the area one gallon or liter of stain covers in one coat. It depends on the product and on the wood. Rough-sawn or porous wood soaks up more stain than smooth, planed boards, so the calculator asks for the wood surface:
| Wood surface | Default coverage |
|---|---|
| Smooth | US: 300 ft²/gal Metric: 8 m²/L |
| Rough-sawn | US: 150 ft²/gal Metric: 6 m²/L |
- The US defaults come from the technical data sheet for ZAR Deck and Siding Semi-Transparent Stain: 300 to 400 ft² per gallon on smooth surfaces and 100 to 200 ft² on rough surfaces. The calculator uses the low end for smooth wood and the middle for rough wood.
- The Metric defaults come from the product data sheet for Ronseal Decking Stain: about 8 to 10 m² per liter per coat on smooth planed boards and 6 to 8 m² on rough sawn boards. The calculator uses the low end of each.
- Other US stains list about 150 to 650 ft² per gallon. Behr lists 250 to 300 ft² for the first coat of its Premium Semi-Transparent Waterproofing Stain & Sealer, Olympic lists 250 to 350 ft² for its Maximum stains, Thompson's WaterSeal lists 150 to 400 ft², and Cabot lists ranges up to 650 ft². A thick deck resurfacer covers much less, such as 75 ft² per gallon for Cabot DeckCorrect.
The transparency of a stain doesn't change the default. Olympic lists the same coverage for its semi-transparent and solid stains, and Thompson's WaterSeal lists the same coverage for its transparent, semi-transparent, and solid sealers, so the difference shows up in the number of coats instead. Because stains vary this much, the coverage on your label is the best value to use. If the label gives a range, enter the low end so you don't run short.
Some UK labels give the area for a whole can. Divide it by the liters and enter it in m²/L. For example, a 5 L can that covers up to 24 m² with one coat is 4.8 m²/L. If a label gives a different coverage for each coat, enter the first, lower one. If it gives the area for all coats together, such as a 2.5 L can that covers up to 20 m² with 2 coats, set Coats to 1 and enter that value (8 m²/L).
Coats and extra stain
Follow the number of coats on your stain's label. Many US stains call for one coat: the ZAR data sheet says to apply one coat, Cabot says to apply 1 coat only for its Semi-Transparent Stain + Sealer, and Thompson's WaterSeal says one coat of its wood sealer is enough. The ZAR data sheet adds that more is not better, so the calculator starts at 1 coat with US units.
Some stains need two coats. Behr says 2 coats are required for its Premium Semi-Transparent Waterproofing Stain & Sealer No. 5077, solid color stains such as Olympic Maximum Solid need two coats, and Cabot DeckCorrect needs two. For these, set Coats to 2. UK decking stains and fence treatments are often applied in two coats. Ronseal recommends two coats of its Decking Stain, and Cuprinol lists two coats for its Anti-Slip Decking Stain, so the calculator starts at 2 coats with Metric units. When you switch between US and Metric, the number of coats changes with them unless you've changed it.
Olympic's deck stain guide suggests 1 gallon of stain in any transparency for decks up to 175 ft², and 2 gallons for decks up to 550 ft². That's more than the calculator shows for one coat at 300 ft² per gallon, and the guide doesn't say how many coats or what coverage it assumes. If your label calls for two coats or lists a lower coverage, enter those values.
Buy all the stain you need at once. Cabot and Cuprinol advise mixing all the cans together before you start so the color is even, which you can't do with a can you buy later. Neither gives an amount of extra, so the waste allowance starts at 10%, the same as for paint. You can change it from 0% to 100%.
Stain can sizes
The calculator shows how many of each common can size you need, so you can compare them with the cans in your store.
| Where | Common sizes |
|---|---|
| US | 5 gallons, 1 gallon, and 1 quart |
| UK | 9 L, 5 L, and 2.5 L |
For other sizes, such as a 1 L or 4 L can, or the 3.78 L and 18.9 L cans sold in Canada, enter the volume on the can as the Custom can size.
Examples
A 12 × 16 ft deck
A deck floor 12 ft × 16 ft is 192 ft². With a 10% waste allowance, the total is 211.2 ft². One coat on smooth boards at 300 ft² per gallon takes 211.2 ÷ 300 = 0.70 gallons, so buy one 1 gallon can, or 3 quarts. On rough-sawn boards, at 150 ft² per gallon, it takes 1.41 gallons.
Adding railings and stairs
Add a railing 40 ft long and 3 ft high on both sides (40 × 3 × 2 = 240 ft²) and 5 steps 4 ft wide with an 18 in tread and riser (4 × 1.5 × 5 = 30 ft²). The net area is 192 + 240 + 30 = 462 ft², or 508.2 ft² with 10% added. One coat at 300 ft² per gallon takes 1.69 gallons, so buy 2 one-gallon cans, or 7 quarts.
A fence
A fence 100 ft long and 6 ft high, stained on both sides, is 100 × 6 × 2 = 1,200 ft², or 1,320 ft² with 10% added. One coat at 300 ft² per gallon takes 4.40 gallons, so buy 5 one-gallon cans or one 5 gallon pail.
Metric dimensions
A deck 4 m × 5 m is 20 m², or 22 m² with 10% added. Two coats on smooth boards at 8 m² per liter take 22 × 2 ÷ 8 = 5.50 liters, so buy 2 cans of 5 L, or 1 can of 9 L.
FAQ
About 0.70 gallons, or one 1 gallon can, for a 12 × 16 ft deck floor with one coat on smooth boards at 300 ft² per gallon and 10% extra. Two coats, or rough-sawn boards, double that to 1.41 gallons. Add your railings and stairs as more sections, and enter your stain's coverage for your own amount.
About 4.4 gallons for a fence 100 ft long and 6 ft high stained on both sides, with one coat at 300 ft² per gallon and 10% extra. Enter the length, the height as Width, and Quantity 2 for both sides.
About 300 ft² per coat on smooth boards and 150 ft² on rough-sawn wood, which are the calculator's defaults. Labels range from about 150 to 650 ft² per gallon depending on the product and the wood, and a thick resurfacer can cover as little as 75 ft². UK decking stains list about 8 to 10 m² per liter on smooth boards and 6 to 8 m² on rough sawn ones. Check your label.
Follow your label. Many US stains call for one coat, while solid color stains and some semi-transparent ones call for two. Most UK decking stains call for two.
Yes, if you enter your own values. The defaults are for outdoor deck and fence stain, so enter the coverage on your interior stain's label and its can size as the Custom can size. The calculator uses the same formula.
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