Deck Stain Calculator: Gallons for Your Deck

This calculator estimates how much stain or sealer a deck surface takes. Enter the deck length and width, the coverage per gallon printed on the can and the number of coats; you get the gallons needed, whole gallons to buy and litres.

Formula

Gallons = deck area (ft²) × coats ÷ coverage per gallon (ft²). Gallons to buy = gallons rounded up. Litres = gallons × 3.785.

• l, w: deck surface length and width in feet
• cov: square feet one gallon covers, from the product label
• coats: number of coats the label calls for

Worked Example

A 16 ft × 12 ft deck, 250 ft² per gallon, two coats.

1. Area = 16 × 12 = 192 ft²
2. Gallons = 192 × 2 ÷ 250 = 1.54 gal
3. Buy 2 gallons
4. In litres: 1.536 × 3.785 = 5.81 L

How to use the result

Rough, weathered or very dry wood soaks up more stain than the label’s coverage figure, so the second coat often takes less than the first. Add railings, stairs and benches as extra area: a railing section is roughly its length × height for each side you coat.

Limits and common mistakes

• Coverage varies a lot between products and wood condition; always use the figure on your can.
• Some products want one coat only; follow the label.
• Check the weather window on the label for drying time.

Frequently Asked Questions

How much stain for a 10 x 10 deck?

At 250 ft² per gallon, one coat: 0.4 gal; two coats: 0.8 gal.

Why did I use more than the label said?

Rough or old wood absorbs more; coverage on new smooth wood is higher.

Do I count the stairs?

Yes, add the tread and riser area if you stain them.

How many litres is a gallon?

One US gallon is 3.785 L.

in l | Deck length | ft | 16 | 0 | 1000
in w | Deck width | ft | 12 | 0 | 1000
in cov | Coverage per gallon (from the can) | ft² | 250 | 1 | 2000
in coats | Coats | coats | 2 | 1 | 5
out gal | Stain needed | gal | l * w * coats / cov | 2
out buy | Gallons to buy | gal | ceil(round(gal, 6)) | 0
out lit | Stain needed | L | gal * 3.785411784 | 2