How this calculator works
It adds the deck floor (length × width), the railing at about 5 sq ft of wood per running foot, and about 5 sq ft per stair step. It multiplies by coats, divides by the stain’s coverage, adds waste and rounds up to gallons and quarts.
The default coverage is 200 sq ft per gallon. Penetrating and semi-transparent deck stains typically list 150 to 300 sq ft per gallon on rough or weathered wood, and more on smooth new boards, so check the can. The railing figure assumes a 36″ rail with 2×2 balusters about 5½″ apart and 2×4 top and bottom rails.
deck = length × width
railing = railing length × 5 ft² per ft
stairs = steps × 5 ft² per step
gallons = (deck + railing + stairs) × coats ÷ coverage × (1 + waste)Worked example
A 16′ × 12′ deck has 192 sq ft of boards. 36 ft of railing adds 180 sq ft and four steps add 20, for 392 sq ft. Two coats at 200 sq ft per gallon is 3.92 gallons; with 10% waste that is 4.31 gallons, which the list buys as 4 gallons plus 2 quarts.
Tips before you buy
- Clean the deck with a deck cleaner and let it dry for at least two days before staining; stain will not soak into dirty or wet wood.
- Sprinkle water on the boards: if it beads up, the old finish or mill glaze needs to come off before new stain will penetrate.
- Stain two or three boards at a time along their full length to avoid lap marks where wet and dry stain meet.
- Do railings and balusters first, then the floor, working toward the stairs so you do not stain yourself into a corner.
Questions
- How many square feet does a gallon of deck stain cover?
- Penetrating and semi-transparent stains usually cover 150 to 300 square feet per gallon on weathered wood, more on smooth new boards. Solid deck stains often list 200 to 400 sq ft. Use the figure on your can for the most accurate result.
- Do I need two coats of deck stain?
- Many semi-transparent and solid stains call for two coats, often applied wet on wet. Some penetrating oils are one-coat products and a second coat just sits on the surface, so follow the label.
- How do I measure railing for stain?
- Measure the total running length of railing along every side and the stairs. Balusters and rails add far more surface than their length suggests, which is why the calculator counts about 5 sq ft of wood per foot.
- How long should new wood weather before staining?
- Many stain makers suggest waiting until new pressure-treated lumber is dry enough to absorb water, which can take weeks to months. Do the water drop test: if the boards soak it up, they are ready.