Deck Stain Calculator
Wondering how much deck stain you need? Our free deck stain calculator turns your deck's length, width, railing and stair area, and the stain's coverage rate into the exact gallons required — then rounds up so you know exactly how many gallons (or quarts) to buy.
Enter your numbers
Your results
| Total stainable area | — |
| Area with coats applied | — |
| Exact gallons (1 decimal) | — |
Tip: also pick up a gallon of deck cleaner/brightener — stain bonds best to clean wood, and most one-day stain jobs start with a wash.
How to use this calculator
Measure your deck's length and width in feet and enter them above. If you have railings, stairs, or benches, estimate their area in square feet and add it as extra area — or measure later and add it in. Set the coverage rate from your stain can (most list 150–400 sq ft per gallon) and choose 1 or 2 coats. Your results update instantly.
When in doubt, lower the coverage number: old, weathered wood drinks noticeably more stain than new boards, and vertical surfaces like railings and stair risers absorb more than the flat deck floor.
How it works
The math is straightforward: gallons = (length × width + extra area) × coats ÷ coverage. A 12×16 ft deck is 192 sq ft; at 250 sq ft per gallon, two coats need 192 × 2 ÷ 250 = 1.54 gallons.
Coverage varies because stain is absorbed, not just spread. The can's rated range of 150–400 sq ft per gallon assumes ideal conditions — new, smooth, horizontal wood. Old, porous, or rough-sawn wood pushes toward the low end of that range, and vertical surfaces (balusters, railings) soak up more per square foot than floor boards. The calculator rounds your purchase up to whole gallons (or quarts under a gallon), so these are working estimates — buy one extra can for big weathered decks.
Frequently asked questions
How much stain do I need for a 12x12 deck?
A 12x12 deck has 144 square feet of floor. At a typical coverage of 250 sq ft per gallon, two coats need 144 × 2 ÷ 250 = about 1.2 gallons, so buy 2 gallons. Add extra for railings, stairs, and benches — and old, thirsty wood can drink noticeably more than new boards.
Is one coat of deck stain enough, or do I need two?
Most manufacturers recommend two coats for new, weathered, or stripped wood: the first coat soaks in and seals the grain, while the second builds the even, protective film. For a maintenance recoat over sound existing stain, one coat is usually enough. Check the can — some solid stains specifically call for a single coat.
How often should I restain my deck?
Every 2 to 4 years in most climates — sooner in full sun, heavy rain, or harsh winters. The splash test is the simplest check: sprinkle water on the deck — if it soaks in instead of beading up, the protection is gone and it’s time to restain.
What is the difference between deck stain and sealer?
Deck stain adds pigment, which gives color and blocks UV rays so the wood doesn’t gray as fast. A clear sealer (water repellent) guards against moisture but lets the wood weather to a natural silver. Many modern products are stain-and-sealer combos that do both jobs in one can.
Can I stain a wet deck?
No. Stain can’t absorb evenly into wet wood, which leads to blotchy color and poor adhesion. Wait at least 24–48 hours after rain, make sure the wood feels dry, and stain when it’s roughly 50–90°F with no rain forecast for a day or two.