Deck Stain Calculator
Estimate stain or sealer for a deck. The floor is the easy part — railings quietly add about 4 ft² of surface for every linear foot once you count both faces and every baluster. Enter your deck size, railing run, and the condition of the wood to get gallons and cost.
Your project
Estimate
3gal
Stain needed · Rounded up to the next half gallon
- Total surface to stain
- 352ft²
- Deck floor area
- 192ft²
- Estimated stain cost
- $126.00
Estimates are guidance only and exclude tax, labor, and site conditions unless stated. Confirm with a local pro.
How it's calculated
No black boxes — here is the exact math behind your estimate, so you can check it or adapt it for your own quote.
- 1
Deck area (ft²) = deck length × deck width - 2
Railing area (ft²) = railing linear feet × 4 - 3
Total surface = deck area + railing area - 4
Gallons = total surface × coats ÷ coverage, rounded up to the next half gallon - 5
Cost = gallons × price per gallon
Worked example
A 16 ft × 12 ft deck with 40 linear feet of railing, new smooth decking, two coats of stain.
Inputs
- Deck length
- 16 ft
- Deck width
- 12 ft
- Railing length
- 40 ft
- Wood condition
- 250
- Coats
- 2
- Price per gallon
- 42 $/gal
Result
- Stain needed
- 3 gal
- Total surface to stain
- 352 ft²
- Deck floor area
- 192 ft²
- Estimated stain cost
- $126.00
Tools & materials for this project
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- Deck stain applicator pad Pole-mounted pad spreads an even coat far faster than a brush.
- Deck cleaner & brightener Strips gray weathered fibers and resets the wood so stain can soak in.
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Frequently asked questions
Transparent, semi-transparent, or solid — which lasts longest?
Pigment is what blocks UV, so the more opaque the finish, the longer it survives. Clear sealers and toners typically last about a year on the deck floor, semi-transparent stains 2–3 years, and semi-solid or solid stains 3–5 years. The trade-off is failure mode: transparent finishes fade and simply need recoating, while solid stains form a film that eventually peels, so the next refinish means stripping or sanding. Railings and vertical surfaces often last twice as long as the floor because they take no foot traffic and less standing water.
How do I tell if my deck actually needs re-sealing?
Use the water-drop test. Sprinkle water on several boards — pick the sunniest spot, a traffic lane, and a shaded area. If the drops bead up and sit for 10 minutes, the finish is still working and you can wait. If the water soaks in and darkens the wood within a minute or two, the deck is ready to clean and recoat. Gray, fuzzy fibers or splintering also mean the surface is spent. Test in multiple places: south-facing boards and the path from the door usually fail a year before the rest of the deck.
Why should I never stain a deck in direct sun?
Hot boards flash off the carrier before the stain can penetrate. Above roughly 90°F surface temperature the stain sets while you are still spreading it, which leaves lap marks, dark overlap streaks, and sticky puddles that stay tacky for days. Work in shade or on an overcast day, in the 50–90°F range, with no rain forecast for 24–48 hours. Follow the shade around the deck rather than fighting it. Wood moisture matters too: wait 24–48 hours after rain or washing so the boards are dry enough to absorb.
Do I have to clean and brighten the wood first?
Yes — stain only penetrates clean, open wood. Wash with a dedicated deck cleaner to lift dirt, mildew, and the gray surface layer, rinse thoroughly, then follow with an oxalic-acid brightener, which neutralizes the cleaner and restores the wood pH and color. Let the deck dry 24–48 hours before staining. On new pressure-treated lumber, skip the old "wait a year" advice and use the water-drop test instead: mill glaze and factory moisture often keep new boards from absorbing for a few weeks to a few months.
How much stain does a 16 × 12 deck need?
The floor is 192 ft², and 40 linear feet of railing adds about 160 ft², for 352 ft² total. On new smooth decking at 250 ft² per gallon, two coats need roughly 3 gallons — about $126 at $42 a gallon. On weathered or rough-sawn wood at 175 ft² per gallon, the same deck takes about 4.5 gallons. Apply the second coat wet-on-wet inside the window on the label; piling dried stain onto an already saturated board leaves a sticky film that never fully cures.