Deck Stain Calculator

How to calculate how much deck stain you need

Running out of stain halfway across a deck is the fastest way to end up with a visible lap line, and buying three cans for a one-can job wastes money. The estimate comes down to three things: the area you are staining, how thirsty the wood is, and how many coats you plan to apply.

Multiply the deck length by its width for the floor area, add an allowance for railings if you have them, multiply by the number of coats, and divide by the coverage rate of your stain. A 16 × 12 ft railed deck is 192 sq ft, about 230 sq ft with railings; two coats on weathered wood at 200 sq ft per gallon works out to roughly 2.3 gallons — so you buy 3.

Why coverage varies so much

• Smooth or previously sealed boards absorb little, so a gallon can cover around 300 sq ft.
• Weathered, rough, or bare wood drinks stain — expect closer to 200 sq ft per gallon, less on a bare first coat.
• The second coat always goes further than the first, because the wood is already sealed.

Don't forget the railings

Balusters, rails, and posts hold a surprising amount of surface for how little floor they take up. Adding about 20 percent to the floor area covers a typical railing without measuring every spindle. A deck with heavy or double railings, or lots of stairs, may need a little more.

Frequently asked questions

How many coats of deck stain do I need? Most semi-transparent and solid deck stains are designed for two coats; many penetrating oil stains are applied as a single saturating coat. Follow the can — over-applying a penetrating stain leaves a sticky film that never fully cures.

How much does a gallon of deck stain cover? Roughly 200 to 300 square feet per coat, depending on the wood. Smooth, sealed boards land near the top of that range; rough or bare wood near the bottom, sometimes less on the first coat.

Should I buy a little extra? Yes — buy all your stain at once from the same batch. Color can shift slightly between manufacturing lots, and a mid-project run to the store for a different batch can leave a visible seam. A little left over is cheap insurance.

Can I use this for a fence or siding too? The coverage math is the same — area times coats divided by coverage per gallon. Just measure the actual surface and skip the railing allowance. See our painting and decorating guides for more.