16 by 20 deck
Includes railing allowance.
4 gallonsStain to buystain calculator deck
Deck Stain Calculator
Deck stain needs depend on square footage, number of coats, wood condition, and the product label coverage rate.
Inputs
Results
Immediate estimateStain to buy4 gallons3.52 gal calculated
Deck surface320 sq ft
Total coated area800 sq ft
Base stain3.2 gal
Waste allowance0.32 gal
Shopping list
- 4 gallons Deck stain
Diagram
Deck stain coverage
Deck boards plus rail and stair allowance are multiplied by coat count.
- Deck surface
- Rail allowance
- Coats
How this calculator works
Estimate how many gallons of deck stain to buy for deck boards, railings, stairs, and multiple coats.
Formula
Deck area and railing allowance are multiplied by coat count, divided by coverage, adjusted for waste, and rounded to whole gallons.
Surface area
deck length × width + rail/stair allowanceCoated area
surface area × coatsGallons
coated area ÷ coverage, plus waste, rounded upAssumptions
- Coverage: Use the product label when it differs from the default.
- Deck condition: Older or rough lumber can absorb more stain.
Worked examples
High coverage label
Shows coverage note.
1 gallonsStain to buyFAQ
Does old wood need more stain?
Often yes. Rough, dry, or weathered wood can absorb more than the label average.
Does this include both sides of railings?
Use the railing allowance field to include any railing, stair, or vertical surface area you expect to coat.
Sources and review
- Paint estimator guidance, PaintCare. Accessed 2026-07-16.
Reviewed 2026-07-16. Planning estimates only; confirm project-specific requirements.