Deck Stain Calculator
Enter your deck dimensions and railing length to find how much stain to buy — including the thirsty first coat.
Runs entirely in your browser — your numbers never leave this page.
How it works
Deck stain math is area math — the trick is that railings count for more than they look:
Gallons = (deck sq ft + railing ft × 3.5) × coats ÷ coverage
- Railings: balusters, top rail, and both faces — roughly 3.5 sq ft per linear foot of railing.
- Coverage: deck stains cover ~200–300 sq ft/gal per coat. We use 250; weathered or thirsty wood needs the low end.
- Two coats on bare/new wood; one maintenance coat on previously stained decks in good shape.
- 10% waste for drips, brush loading, and the can bottom you'll never quite empty.
- Buy one batch: mix all cans together (boxing) so color is uniform across the deck.
Frequently asked questions
How much stain for a 20x14 deck?
280 sq ft deck + railings ≈ 350–420 sq ft per coat. Two coats at 250 sq ft/gal ≈ 3 gallons — buy 3–3.5 with waste.
How many square feet does a gallon of stain cover?
Typically 200–300 sq ft per coat. New or weathered wood absorbs more (use 200); smooth previously-stained wood uses less (up to 300).
One coat or two?
Two on bare or stripped wood; one maintenance coat on decks stained within the last 2–3 years and still in good shape.
Do railings really need that much stain?
Yes — balusters have huge surface area. Budget ~3.5 sq ft per linear foot of railing, both faces included.
Stain or paint for a deck?
Stain penetrates and won't peel — better for horizontal surfaces that take weather. Paint looks crisper but peels on decks.
When is the best time to stain?
Dry wood, 50–90°F, no rain for 24–48 hours. Spring and fall beat summer heat (stain dries too fast and laps show).
How long does deck stain last?
Transparent: 1–2 years; semi-transparent: 2–3; solid: 3–5. Horizontal surfaces wear faster than railings.
Should I pressure wash first?
Yes — clean, dry wood absorbs evenly. Let it dry 24–48 hours after washing before staining.
Can I mix stain cans?
Yes — "boxing" (mixing all cans together) is recommended so color stays uniform across the deck.
Oil or water-based stain?
Oil penetrates deeper and is more forgiving; water-based dries fast, cleans up with soap, and holds color longer. Both work — don't mix them.