Estimate how much stain or sealer to buy for your deck. Enter the deck size, railing length and stairs, choose the number of coats and the condition of the wood, and get the gallons and liters you need, which cans to buy and what it will cost.
Last updated:
Units
ft
m
ft
m
ft
0 if no railing
m
0 if no railing
ft
m
Stain
Sq ft per gallon (m² per liter in metric) from the can; overrides the estimate
$
Enter your values to see the result.
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How to use the Deck Stain Calculator
Enter the deck length and width in feet or meters.
Add the railing length and type and the number and width of stair steps.
Choose the number of coats, wood condition and product, or type the coverage from the can.
Enter the price per gallon and read how much stain to buy and what it costs.
How the stain amount is calculated
Floor = length × width
Railing = railing length × surface factor (≈ 4 sq ft per ft with balusters, 6 for solid boards, 1 for cable or glass)
Stairs = steps × stair width × (11.25 in tread + 7.25 in riser)
Gallons = area ÷ first-coat coverage + (coats − 1) × area ÷ (1.5 × coverage), plus 10%
Example: a 20 × 12 ft deck (240 sq ft) with 44 ft of baluster railing (176 sq ft) and three 4 ft steps (18.5 sq ft) has 434.5 sq ft. On weathered wood at 175 sq ft/gal, two coats need 2.48 + 1.66 = 4.14 gal, or about 4.6 gal with 10% extra.
Typical deck stain coverage (first coat)
Wood surface
Sq ft per gallon
m² per liter
New, smooth, kiln-dried
200–300
4.9–7.4
Weathered or previously stained
150–200
3.7–4.9
Rough-sawn or very porous
100–150
2.5–3.7
Second coat (most products)
about 1.5× the first coat
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Prep tips
Clean the deck and let it dry for 24–48 hours; new pressure-treated wood may need weeks to dry before it absorbs stain.
Do the water drop test: if water soaks in within a few minutes, the wood is ready.
Stain in shade at mild temperatures and keep a wet edge, working the full length of a few boards at a time.
Frequently asked questions
How much stain do I need for a 12×12 deck?
A 12 × 12 ft deck floor is 144 sq ft. On weathered wood at about 175 sq ft per gallon, one coat takes roughly 0.8 gal and a second coat about 0.55 gal, so with 10% extra you need about 1.5 gallons for two coats, before any railing or stairs.
How many square feet does a gallon of deck stain cover?
Most penetrating deck stains cover about 150–300 sq ft per gallon. Smooth, new wood is at the high end; weathered or rough-sawn wood soaks up more and can drop to 100–150 sq ft. Always check the coverage on the can, and enter it in the calculator to override the estimate.
How do I estimate stain for railings?
Railings with balusters have a lot of surface: with both sides of the balusters, the top and bottom rails and the posts, a typical 36 in railing works out to about 4 sq ft of surface per linear foot. A railing made of solid boards is about 6 sq ft per foot (both sides), and cable or glass railings only need the wood frame stained.
Do I need two coats of deck stain?
Transparent and semi-transparent stains often need one or two thin coats, applied wet-on-wet or as the label says; overapplying can leave a sticky film. Solid stains usually need two coats. The second coat covers more area per gallon because the wood is already partly sealed; the calculator assumes about 1.5 times the first-coat coverage.
How much does it cost to stain a deck?
Deck stain typically costs about $30–$70 per gallon. A 20 × 12 ft deck with railing and stairs needs about 4–5 gallons for two coats on weathered wood. Enter your own price to see the total and the cost per 100 sq ft.
Should I buy 1 gallon or 5 gallon containers?
Five-gallon pails are usually cheaper per gallon and avoid color differences between cans, so buy them for large jobs and use a 1 gallon can for the remainder. If you buy several 1 gallon cans, mix (box) them together first for an even color.
Is my data sent anywhere?
No. All calculations run in your browser.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.