About the Deck Stain Calculator
This deck stain calculator estimates how much stain, sealer or deck paint you need for a whole deck — not just the floor, but the railings and steps that people usually forget. Enter the deck size, railing length and height, the number of steps and the coverage printed on the can, and it returns the total area, gallons for the coats you plan, a sensible mix of 5-gallon pails and 1-gallon cans to buy, and the cost.
It is for homeowners refinishing a deck, DIYers planning a weekend clean-and-stain job, and contractors pricing a re-stain. The estimate works for transparent, semi-transparent and solid stains and for clear water-repellent sealers — only the coverage figure changes.
Coverage varies a lot with the wood: new smooth boards may take 250–300 sq ft per gallon, while weathered, rough or very porous wood can drink stain at 100–150 sq ft per gallon. Always check the label, and remember that a second coat usually goes further than the first. Spindle railings are counted at 1.5 times their face area to cover all four sides of each baluster plus the top and bottom rails.
With the default inputs, the stain needed is 4.36 gal. Change any value above to recalculate instantly.
How to use the deck stain calculator
- 1Measure the deck length and width in feet.
- 2Add the total length and height of any railings, and the number and width of steps.
- 3Enter the coverage per gallon from the stain label and how many coats you will apply.
- 4Add an extra allowance — 10% for average wood, 20–30% for rough or weathered boards.
- 5Read the gallons needed, what to buy and the total cost.
Formula and method
The deck floor is its length times width. A spindle railing has far more surface than its outline suggests: with 2x2 balusters about 4 inches apart, the four sides of every baluster plus the top and bottom rails add up to roughly 1.5 times the railing’s length × height, so that factor is used. Each step counts an 11-inch tread plus a 7½-inch riser across the stair width.
The total area is multiplied by the number of coats and by the extra allowance for porous wood and waste, then divided by the coverage per gallon from the product label. The result is the stain you will use; the purchase suggestion rounds up to whole containers, switching to a 5-gallon pail when you would otherwise need more than three single gallons, which is usually cheaper per gallon.
- L, W
- Deck length and width (ft)
- Rail, H
- Railing length (ft) and height (in)
- Ws
- Stair width (ft)
- Coverage
- Square feet per gallon per coat
Worked examples
16 × 12 ft deck with railing and four steps, two coats
The floor is 192 sq ft, the 40 ft railing at 3 ft high counts as 40 × 3 × 1.5 = 180 sq ft, and four 4-ft steps add 4 × 4 × 18.5/12 = 24.7 sq ft, for 396.7 sq ft. Two coats plus 10% extra at 200 sq ft/gal needs 396.7 × 2 × 1.1 ÷ 200 = 4.36 gallons, so one 5-gallon pail ($225 at $45/gal).
Large weathered deck, one coat of sealer
A 24 × 20 ft deck is 480 sq ft with no railing or stairs. Rough wood covers only 150 sq ft per gallon, so one coat with 20% extra needs 480 × 1.2 ÷ 150 = 3.84 gallons. Rather than four single gallons, the calculator suggests one 5-gallon pail ($175 at $35/gal), which is usually cheaper per gallon and leaves some for touch-ups.
Wraparound deck with long railings
The floor is 420 sq ft, 90 ft of 42-inch railing is 90 × 3.5 × 1.5 = 472.5 sq ft, and six 5-ft steps add 46.25 sq ft. Two coats at 250 sq ft/gal with 10% extra need 938.75 × 2 × 1.1 ÷ 250 = 8.26 gallons, so two 5-gallon pails (10 gallons, $500).
Frequently asked questions
How much deck stain do I need per square foot?+
Most deck stains cover about 150–300 square feet per gallon per coat. A typical 200 sq ft/gal product means a 12 × 16 ft deck floor (192 sq ft) needs about 1 gallon per coat, before railings and stairs. Rough, old or dry wood can halve the coverage.
How much stain do deck railings take?+
More than most people expect. Because every baluster has four sides, a spindle railing has roughly 1.5 times as much surface as its length × height. Forty feet of 36-inch railing is about 180 sq ft — nearly as much as the floor of a 12 × 16 deck.
Should I apply one or two coats of deck stain?+
Follow the label. Many semi-transparent and solid stains recommend two thin coats applied wet-on-wet or a few hours apart, while penetrating oil stains and clear sealers often call for one coat on dense wood. The second coat usually needs less product than the first because the wood is already partly saturated.
Is it cheaper to buy deck stain in 5-gallon pails?+
Usually — most brands price the 5-gallon pail below five single gallons, so compare the per-gallon price at your store. If you need more than about three gallons, a pail is normally the better buy, one batch keeps the colour consistent, and leftover stain keeps for touch-ups if sealed tightly.
How do I measure a deck for staining?+
Multiply the deck length by width for the floor. Measure the total linear feet of railing and its height, and count the steps and their width. Include benches, planters and skirting separately by adding their face areas to the deck size.