Deck Stain Calculator
Calculate how many gallons of stain you need for a deck, plus total cost at your price per gallon.
How this calculator works
Deck stain coverage is measured per gallon over the deck’s total surface area. This calculator divides your deck’s square footage by 250 square feet per gallon — the standard rate for one coat on smooth, previously finished decking.
Formula: Gallons = Deck area (sq ft) ÷ 250 sq ft per gallon.
Worked example
A 20 ft x 15 ft deck (300 sq ft), $40/gallon:
- Gallons: 300 ÷ 250 = 1.20 gallons
- At $40/gallon, that’s $48.00 for one coat.
Coverage reference
| Deck area | Gallons needed (1 coat) |
|---|---|
| 100 sq ft | 0.4 gallons |
| 300 sq ft | 1.2 gallons |
| 500 sq ft | 2.0 gallons |
How to measure your deck
Measure the deck’s length and width in feet and multiply for total square footage, adding stairs or attached landings as separate rectangles if you’re staining those too. New or bare wood should get two coats as standard practice, and rough or weathered boards absorb more stain than smooth ones — so treat the 250 sq ft/gallon rate as a starting point for smooth, previously-finished decking and adjust down for older or textured surfaces.
Frequently asked questions
How much deck area does one gallon of stain cover?
About 250 square feet for one coat on smooth, previously-finished decking. This calculator divides your deck's total area by that rate to get gallons needed.
Does rough or weathered wood need more stain?
Yes — rough-sawn, textured, or weathered decking is more porous and absorbs considerably more stain, typically dropping coverage to roughly 150-200 square feet per gallon instead of 250. Budget for extra stain if your deck hasn't been refinished in several years.
How many coats of stain does a new deck need?
Two coats is the standard recommendation for new or bare wood, since the first coat mostly gets absorbed into the fibers and the second builds the protective, even-colored finish. Multiply this calculator's result by two if you're staining new lumber.
Should I include railings and stairs in my deck area?
Yes, if you're staining them too — railings, balusters, and stair stringers all add surface area beyond the flat deck boards, and their irregular shapes tend to use more stain per square foot than flat decking. Add an estimate for that surface area to your total before calculating.
Why isn't waste added by default for deck stain?
Stain is a liquid applied evenly across the surface with a brush, roller, or sprayer, so there's no cut-off scrap the way there is with board or sheet materials. Any extra needed for a second coat or a more absorbent surface should be added by adjusting the coverage assumption or multiplying by your coat count, not through a waste percentage.
Estimates only. Verify quantities with your supplier before purchasing.