Deck Stain Calculator
Gallons of stain for a deck, including railings and coats.
Total run of railing. Enter 0 for a ground-level deck without rails.
From the can. Use 150 to 200 for old or rough wood, 250 to 300 for smooth new wood.
You need
2.3 gallons
Buy 3 gallon(s). Leftover stain is useful for annual touch-ups.
- Deck surface
- 192 sq ft
- Railing surface
- 98 sq ft
- Total area to coat
- 580 sq ft
Estimates only. Verify quantities before ordering.
How this is calculated
Stainable area = (deck length x width) + (railing length x 3.5). Gallons = area x coats / coverage per gallon. The purchase figure rounds up to whole gallons.
Enter your deck's dimensions and the total length of railing, and this calculator estimates the stain you need. Railings are the part everyone underestimates: balusters, rails, and posts add a surprising amount of surface, so the calculator converts each linear foot of railing into about 3.5 square feet of stainable area.
Coverage varies more with stain than with paint. New, smooth wood might take 250 to 300 square feet per gallon, while old, weathered, or rough-sawn boards can drink stain at 150 square feet per gallon. The first coat always absorbs more than the second. Check the can and adjust the coverage field to match your product and the condition of your wood.
Stain for common deck sizes
Rows assume two coats at 250 sq ft per gallon, with a railing run typical for each deck size. Round up to whole gallons.
| Deck size | Gallons | Area to coat |
|---|---|---|
| 10 x 10 ft, 24 ft railing | 1.5 gallons | 368 sq ft |
| 12 x 12 ft, 28 ft railing | 1.9 gallons | 484 sq ft |
| 16 x 12 ft, 32 ft railing | 2.4 gallons | 608 sq ft |
| 20 x 14 ft, 40 ft railing | 3.4 gallons | 840 sq ft |
| 20 x 16 ft, 44 ft railing | 3.8 gallons | 948 sq ft |
Opacity: clear through solid
Deck finishes run a spectrum from clear sealer to solid stain, and the choice trades appearance against lifespan. Clear sealers repel water and show all the wood grain, but with little or no pigment they offer almost no ultraviolet protection, so the wood grays underneath and they need reapplying most often, often annually.
Toners and semi-transparent stains add pigment while still showing grain. Pigment is what blocks ultraviolet light, so each step toward opacity buys longevity: semi-transparent typically lasts two to three years on a deck floor. Semi-solid and solid stains hide most or all of the grain and can last three to five years, though solid stain on a horizontal surface eventually peels rather than fading, which means scraping and sanding at renewal rather than a simple recoat.
The decision is largely one-way. You can always go more opaque later, but you cannot return to a lighter or clearer finish without stripping or sanding the whole deck. Starting semi-transparent leaves your options open.
Preparation and moisture
Adhesion depends on preparation more than product. Clean the deck with a dedicated deck cleaner to remove dirt, mildew, and the gray oxidized surface layer, and follow with a brightener if the cleaner was alkaline, which restores the wood pH so the stain absorbs evenly. Pressure washing is effective and easy to overdo: too much pressure furs the wood fibers and leaves a surface that drinks stain unevenly.
New pressure treated lumber needs to dry before it takes a finish, which can mean anywhere from several weeks to several months depending on how wet it was when milled and on the weather. Test with a few drops of water: if they bead and sit, the wood is still too wet or too dense to absorb stain; if they soak in within a minute, it is ready.
Check the forecast for 48 hours in both directions. Staining over damp wood traps moisture and causes early peeling, and rain within a day of application washes the finish off before it has cured.
Application and recoating
Work in the shade and follow the sun around the deck rather than staining in direct heat, which flashes the carrier off before the finish penetrates. Coat two or three boards at a time along their full length so that you always maintain a wet edge; stopping mid-board leaves a lap mark that stays visible for the life of the finish.
More is not better with penetrating stains. Apply what the wood absorbs and wipe off anything still sitting on the surface after 15 minutes or so, because unabsorbed stain dries into a sticky film that peels. Solid stains behave more like paint and do build a film, so they follow paint rules instead.
Recoat on condition rather than a calendar. Sprinkle water on the deck: if it soaks straight in rather than beading, the finish is spent. Horizontal surfaces and south-facing rails always fail first, and spot recoating those areas as they wear extends the interval before the whole deck needs doing.
Common questions
How many coats of deck stain do I need?
Transparent and semi-transparent penetrating stains usually take one to two thin coats; a second coat should go on before the first fully dries so it can still absorb. Solid stains behave more like paint and typically need two coats. Never build thick layers of penetrating stain, since the excess will not soak in and stays sticky.
How do I know when my deck needs re-staining?
Sprinkle water on the boards. If it beads up, the finish is still repelling water. If it soaks in and darkens the wood within a couple of minutes, the protection is gone and it is time to clean and re-stain. Most horizontal deck surfaces need re-coating every 2 to 3 years.
Do I have to strip the old stain first?
If you are re-coating with the same type and a similar or darker color, a thorough cleaning is usually enough. Switching from solid to transparent stain, or dealing with peeling, requires stripping or sanding back to bare wood, because transparent products cannot hide or bond over a failing solid film.
How long should a new deck dry before staining?
Pressure-treated lumber needs to dry out before it will accept stain, typically 1 to 3 months depending on climate and how wet the boards were at purchase. Use the water test: when droplets soak in rather than bead on the surface, the wood is ready.