Enter the size of the deck, the length and height of the railings and the coverage printed on your stain. The calculator adds the floor and both faces of the railing and gives the gallons for the coats you plan.
Deck stain formula
Floor = length × width Railings = railing length × height × 2 sides Gallons = (floor + railings) × coats ÷ coverage per gallon
Worked example: a 16 × 12 ft deck with 40 ft of railing
- Floor: 192 sq ft.
- Railings: 40 × 3 × 2 = 240 sq ft.
- One coat at 200 sq ft per gallon: 432 ÷ 200 = 2.16 gallons, so buy 3.
About coverage
Coverage varies a lot between stains and with the wood: new, smooth boards absorb less than old, weathered or rough-sawn wood, and solid stains often cover more than transparent ones. The 200 sq ft default is only a starting point; use the coverage on your can, and the low end of its range for weathered wood. Railings are a rough area estimate; balusters and lattice have more surface than a flat panel, so add extra if your railing is spindles.
Tips
- Clean and dry the deck first; follow the stain’s instructions on prep and dry time.
- Stairs: add each tread and riser to the floor area.
- Test on a hidden board to check color.
Questions
How much stain for a 12 × 12 deck?
144 sq ft of floor needs 0.72 gallons for one coat at 200 sq ft per gallon, plus the railings.
Do I need two coats?
It depends on the product; many semi-transparent stains are applied in one or two coats. Follow the label.
Does this work for fences?
Yes. Enter the fence length and height as the railing; both faces are counted.
Sources
- NIST Guide to the SI, Appendix B.8: Factors for units listed alphabetically, National Institute of Standards and Technology.
Used for: Square foot definitions.