Deck Stain Coverage Calculator

How much stain your deck actually needs

The label on a can of deck stain usually promises 250 to 350 square feet of coverage per gallon. In practice, most homeowners get closer to 200 sqft per gallon on new smooth wood and 150 sqft per gallon on weathered or rough-sawn wood. The porosity of aged pressure-treated pine soaks stain the way a sponge soaks water — especially on the first coat.

Don't forget the vertical surfaces

The deck floor is usually 60–70% of the total surface you'll be staining. Railings, balusters, stair risers, and fascia can easily add 40% more surface area. The calculator above accounts for the walking surface — add 30–40% to the gallon count if you're also finishing rails and stairs the same day.

One coat or two?

Most semi-transparent penetrating stains (Cabot Australian Timber Oil, TWP) are single-coat by design — a second coat sits on top and peels within a season. Solid stains and film-forming finishes typically require two coats, applied wet-on-wet before the first coat dries completely. Read the label of your specific product before you buy — the coverage rate and coat count on the calculator assumes single-coat semi-transparent, the most common choice.

Ready Seal: how many gallons

Ready Seal is the exception to the one-coat rule: on rough or weathered wood it is applied as two light coats, wet-on-wet, with the second going on while the first is still tacky. Its distributor puts the first coat at roughly 125 sqft per gallon on rough or weathered wood (up to 250 on smooth, planed boards) and the second coat at about 250 sqft per gallon, because it lands on wood that is already sealed. To use the calculator for Ready Seal, run it once at 1 coat and 125 sqft coverage, again at 1 coat and 250, and add the two. A weathered 16 × 12 ft deck (192 sqft) takes 192 ÷ 125 + 192 ÷ 250 = 2.3 gallons; add 40 ft of railing (about 80 sqft) and it is 3.3 gallons — one 5-gallon pail rather than four 1-gallon cans. On smooth new boards that are ready to take stain, one moderate coat at about 250 sqft per gallon is usually enough.

How many gallons of stain for common deck sizes

These are floor only. Add about 2 sq ft per linear foot of railing and the stair treads and risers, then round up to whole cans. Using a specific brand such as Cabot, Behr or Ready Seal? Enter the spread rate from that product's label or data sheet as the coverage — the calculator does the rest.

Buffer factor

Always buy 15% more stain than the math suggests. Reasons: spilled cups, wind-blown drips, corner touch-ups, and the inevitable "I'll do one more pass on that spot" the day after. Unopened cans of stain sit for years and are useful for spot repair — buy the buffer, don't try to run tight.

Timing the job right

New pressure-treated lumber needs to dry 4–8 weeks before stain will penetrate. Test by putting a drop of water on the board — if it beads for more than 60 seconds, wait another two weeks. Fresh cedar and hardwoods can be stained sooner but still benefit from 2–3 weeks of drying after the deck is complete. Combine the stain job with a proper wash-and-brighten routine (see our deck cleaner guide) for a finish that actually lasts.