The Deck Paint & Stain Calculator works out how many gallons of stain or deck paint you need for the deck boards, railings and stairs, and what it will cost.
Deck Paint & Stain Calculator
Gallons of deck stain or paint for the deck boards, railings and stairs — plus cost.
Stairs assume 11 in treads and 7.5 in risers.
Railings are counted on both sides, and stairs include both treads and risers. Coverage varies a lot with the wood, its age and the product — stains are commonly listed around 150–300 ft² per gallon — so use the figure on your product label.
Formula
Area = L × W + 2 × railing length × railing height + steps × stair width × (11 + 7.5) ÷ 12
Stain = area × coats ÷ coverage
Cost = whole gallons × price
Stairs assume 11 in treads and 7.5 in risers.
How the Calculation Works
Step 1: Deck surface = length × width.
Step 2: Railings = length × height × 2 sides (treated as a solid face).
Step 3: Stairs = steps × width × (tread + riser).
Step 4: Multiply by coats, divide by coverage, round up to gallons.
Example Calculation
Given (example price): 16 × 12 ft deck, 40 ft of railing 3 ft high, 4 steps 4 ft wide, 2 coats, 250 ft²/gal, $40/gal
- Deck = 192 ft²
- Railings = 40 × 3 × 2 = 240 ft²
- Stairs = 4 × 4 × 1.54 ≈ 24.7 ft²
- Total ≈ 456.7 ft² → × 2 ÷ 250 ≈ 3.65 gal → 4 gallons → $160
Material Estimation Notes
- New, rough or weathered wood absorbs more; smooth or previously coated wood less.
- Spindle railings have less surface than a solid face but take more time; the calculator’s solid-face estimate errs on the safe side.
- Many stains are applied in one or two coats — follow the product instructions.
- Deck cleaner and brightener are separate products.
Frequently Asked Questions
How much stain do I need for my deck?
Deck + railings + stairs area × coats ÷ coverage.
How many gallons of stain for a 12 × 16 deck?
For the boards alone at 250 ft²/gal and two coats: 192 × 2 ÷ 250 ≈ 1.5 gallons; railings and stairs add more.
How much does a gallon of deck stain cover?
Check the label; coverage depends on the wood and product.
Should I count both sides of the railing?
Yes if you coat both sides — the calculator does.
Is deck paint calculated the same way?
Yes, with the paint’s coverage rate.