Calculators · Stain Calculator
Decks & FramingStain Calculator
Add your deck, fence, railings and steps, pick a product and get the gallons of wood stain to buy. Coverage comes from the manufacturers.
Stain needed
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How to calculate how much stain you need
Stain is sold by the gallon and each product states how many square feet one gallon covers. The calculation measures the wood surface, applies the coverage of your product and rounds up to whole gallons.
| Surface | Area formula |
|---|---|
| Deck floor or flat surface | length (ft) × width (ft) |
| Fence or wall | length (ft) × height (ft) × sides stained (1 or 2) |
| Railing | total length (ft) × height (ft) × 2, to count both sides |
| Steps | number of steps × step width × (tread depth + riser height) |
| Gallons | total area × coats ÷ coverage per gallon per coat × (1 + extra ÷ 100), rounded up |
The railing and step formulas are the ones on the stain calculator of Pittsburgh Paints and Stains. TWP says to add the deck floor, the railings and the steps, and to multiply length by height by two for a fence. The calculator reads measurements typed like 10'6" or 10 ft 6 in. When you pick “Steps” the units switch to inches, because treads and risers are measured that way.
Example: a deck with a railing and steps
A deck floor measures 12 ft by 16 ft. It has 20 ft of railing 3 ft high and 4 steps that are 36 inches wide, with an 11 inch tread and a 7 inch riser. You choose Ready Seal on a cedar deck, whose data sheet gives 150 square feet per gallon, one coat and 10% extra.
| Step | Operation | Result |
|---|---|---|
| Deck floor | 12 × 16 | 192 ft² |
| Railing | 20 × 3 × 2 | 120 ft² |
| Steps | 4 × 3 × (11 + 7) ÷ 12 | 18 ft² |
| Total area | 192 + 120 + 18 | 330 ft² |
| Gallons | 330 ÷ 150 | 2.2 gallons |
| With 10% extra | 2.2 × 1.10 | 2.42 gallons |
| Gallons to buy | 2.42 rounded up | 3 gallons |
The same deck with Cabot Semi-Solid Stain, which covers 400 to 500 square feet per gallon, needs 0.91 gallons with the lower figure and 0.73 with the upper one, so 1 gallon either way.
How many square feet does a gallon of stain cover?
The table copies the coverage from three manufacturers, in square feet per gallon, as each page or data sheet gives it. They were checked in October 2026. When a range is given, the calculator uses the lower figure, which means more stain, and shows the result for the upper figure too.
| Product | Sq ft per gallon | Coats on the page |
|---|---|---|
| Cabot Semi-Solid Stain + Sealer | 400 to 500 | 1 |
| Cabot Semi-Transparent Stain + Sealer | 200 to 650 | 1 |
| Cabot Australian Timber Oil | 250 to 600 | 1 |
| Cabot Gold | 250 to 400 | 1 or 2 |
| TWP 100 and 1500 Series | 150 to 200 first coat, 100 to 125 for two coats | Typically 2, wet on wet |
Ready Seal publishes one figure for each type of wood in its data sheet. Its figures include enough stain for new wood, and the sheet adds that older wood is more porous and needs more.
| Wood and surface | Sq ft per gallon | Wood and surface | Sq ft per gallon |
|---|---|---|---|
| Cedar deck | 150 | Spruce fence | 150 |
| Cedar fence | 125 | Pine fence | 150 |
| Cedar shingles | 150 | Pine siding | 170 |
| Cedar siding | 125 | Treated pine deck | 150 |
| Redwood deck | 175 | Treated pine fence | 150 |
Gallons for one coat by area and coverage
Gallons for one coat with no extra. Multiply by the number of coats for a product that gives one coverage figure for every coat.
| Area | 150 sq ft per gallon | 250 sq ft per gallon | 400 sq ft per gallon |
|---|---|---|---|
| 100 ft² | 0.67 | 0.40 | 0.25 |
| 200 ft² | 1.33 | 0.80 | 0.50 |
| 400 ft² | 2.67 | 1.60 | 1.00 |
| 600 ft² | 4.00 | 2.40 | 1.50 |
Tips for ordering
- Add one surface for the floor, one for the railing and one for the steps. Each has its own formula.
- Read the label for the coverage and the number of coats. Type the coverage into “Custom coverage” if your product is not listed.
- Use the extra box for the allowance your installer or the manufacturer recommends. It is added before the gallons are rounded up.
- This calculator is for wood. Concrete stain has its own coverage figures that are not covered here.
- To measure the deck first, use the deck calculator. For a fence, use the fence calculator.
Frequently asked questions
How do I calculate how much stain I need?
Add up the area you will stain in square feet, multiply by the number of coats, divide by the square feet that one gallon covers per coat, and round up. A 12 ft by 16 ft deck floor, a 20 ft railing 3 ft high with both sides stained and four steps add up to 330 square feet. With a stain that covers 150 square feet per gallon and 10% extra, that is 330 ÷ 150 × 1.10 = 2.42 gallons, so 3 gallons.
How many square feet does a gallon of stain cover?
It depends on the product, the wood and the number of coats. The manufacturer pages we checked in October 2026 give 400 to 500 square feet per gallon for Cabot Semi-Solid Stain, 200 to 650 for Cabot Semi-Transparent Stain, 150 to 200 for the first coat of TWP 100 and 1500 Series, and 125 to 175 for Ready Seal depending on the wood. Read the label of your product.
How much stain do I need for a deck?
Add the floor, the railings and the steps. The floor is length times width. A railing is its length times its height times two, to count both sides. Each step is its width times the tread plus the riser. Choose “Flat surface”, “Railing” and “Steps” in the calculator and it adds them for you.
How much stain do I need for a fence?
Multiply the length by the height, and by two if you stain both sides. A fence 100 ft long and 6 ft high with both sides stained is 1,200 square feet. With a coverage of 125 square feet per gallon, which is the Ready Seal figure for a cedar fence, that is 9.6 gallons, so 10 gallons for one coat.
How much area will 1 quart of stain cover?
A quart is a quarter of a gallon, so it covers a quarter of the area. With a stain that covers 400 to 500 square feet per gallon, one quart covers 100 to 125 square feet. For 8 fluid ounces, which is one sixteenth of a gallon, divide the gallon coverage by 16. At 150 square feet per gallon that is about 9 square feet.
How many coats of stain do I need?
It depends on the product. The Cabot pages we checked recommend 1 coat for most of their stains and 1 or 2 for Cabot Gold. The TWP page says its semi-transparent stains are typically applied wet on wet for 2 coats and that new wood less than a year old should get only 1. Choose the number of coats in the calculator. When a product gives its own figure for two coats, as TWP does, the calculator uses it.
How much extra stain should I buy?
Older and more porous wood needs more stain, and the Ready Seal data sheet says its figures include enough for new wood only. How much to add depends on your wood and your product, so ask the manufacturer or your installer. Enter that percentage in the extra box and the calculator adds it before it rounds up the gallons. Leave it empty to add nothing.
How much does stain cost per gallon?
Prices change by brand, type and region, so this calculator does not show them. Take the gallons from the result and ask local suppliers for a quote in the same unit.
More calculators
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- Fence Calculator Count the posts, rails and pickets or panels for a fence with several runs, gates and corners.
- Paint Calculator Find how many gallons of paint your walls and ceiling need, with doors, windows and coats.