Deck Stain Calculator
Estimate how many gallons of deck stain you need for the deck floor, railings and stairs, with coats, coverage per gallon, waste and can sizes.
Work out how many gallons of deck stain to buy for the deck floor, railings and stairs. Enter the deck size, the railing length and the number of steps, then the coverage printed on your stain can. The calculator adds the areas, multiplies by the number of coats, adds a waste allowance and rounds up to 1-gallon cans and 5-gallon pails.
How to use this tool
- Measure the deck length and width in feet.
- Add the total railing length and its height, or enter 0 if there is no railing.
- Enter the number of steps and the stair width.
- Enter the coverage per gallon from the can and choose one or two coats.
- Read the gallons needed and the suggested containers.
Formula
Gallons = (deck + railing + stair area) × coats ÷ coverage × (1 + waste %)
Deck area = length × width. Railing area = railing length × height × 2, counting both faces. Each step counts as stair width × 18.5 inches (an 11-inch tread plus a 7.5-inch riser). Coverage is square feet per gallon for one coat.
Example
A 16 × 12 ft deck is 192 sq ft. With 36 ft of 36-inch railing (36 × 3 × 2 = 216 sq ft) and three 4-ft-wide steps (3 × 4 × 18.5 ÷ 12 = 18.5 sq ft), the total is 426.5 sq ft. Two coats at 200 sq ft per gallon need 4.27 gallons; adding 10% for waste gives 4.69 gallons, so the estimate rounds up to one 5-gallon pail.
Frequently asked questions
How much area does a gallon of deck stain cover?
It depends on the product and the wood. Penetrating stains often list roughly 150–300 sq ft per gallon, while thick resurfacing coatings can cover under 100. Rough, old or very dry boards soak up more, so use the low end of the label range for weathered decks.
Do I need two coats?
Many semi-transparent and solid stains call for two thin coats, while some penetrating oil stains are one-coat products. Follow the label; the calculator simply multiplies the area by the coats you choose.
Why are railings counted on both sides?
The two-panel model is a rough allowance, not an exact baluster measurement. It ignores gaps and individual edges. For an unusual railing, measure the stainable components separately and use that area instead.
Should I buy all the stain at once?
Yes. Tinted stain can vary slightly between batches, so buying every can together and mixing them keeps the colour even across the deck.
Last updated: 2026-10-30