Calculators › Exterior & Framing

Deck Stain Calculator

Work out gallons of stain or sealer for your deck, including railings and stairs.

Enter your measurements

Length × width
0 if no railings; each foot counts ~2 sq ft both sides

Old dry wood on a first coat can drink 40% more than the can claims. Better one leftover quart than a two-tone deck.

How the calculator works

Stain needs are surface area × coats ÷ coverage. The tool adds railing area at 2 sq ft per linear foot (both sides of a standard 36″ rail with balusters, since spindles are all surface area). Coverage presets reflect the single biggest variable: how thirsty the wood is. Weathered, never-sealed decking absorbs far more than the smooth-wood figure printed on the can.

Worked example: a 12 × 16 deck (192 sq ft) with 40 ft of railing (80 sq ft) is 272 sq ft. Two coats on weathered wood at 175 sq ft/gal = 3.1 gallons → buy 4, since the fourth can is the difference between finishing the deck and stopping mid-board.

Transparent, semi, or solid?

  • Clear/transparent sealer: shows the most grain, lasts 1–2 years on horizontals.
  • Semi-transparent: the sweet spot: color plus grain, 2–3 years on deck floors.
  • Solid stain: paint-like film, hides gray wood and mismatched boards, 3–5 years, but commits you: it only recoats with more solid.

Prep determines lifespan

Stain fails from below. Clean with a deck cleaner (not just a pressure blast that furs the fibers), let the wood dry 48 hours, and check absorbency with a splash of water. If it beads, the old finish must come off or the new coat will peel in sheets. New pressure-treated lumber needs 1–6 months of weathering before it will take stain at all. Apply out of direct midday sun, and back-brush: stain flooded on without working in dries shiny and peels early.

Frequently asked questions

How much stain do I need for a 12x16 deck?

About 2.2 gallons for two coats on the 192 sq ft floor alone at typical weathered-wood coverage, call it 3 cans, or 3.1 gallons once you include 40 ft of railings, which means buying 4. Rough, thirsty wood can push it higher.

How long should a new deck dry before staining?

New pressure-treated lumber needs 1 to 6 months of weathering until water soaks in rather than beading. Kiln-dried (KDAT) lumber can be stained right away.

Is one coat of deck stain enough?

For penetrating semi-transparent stains, two thin coats applied wet-on-wet outlast one heavy coat. Solid stains generally specify two. One coat is only right for annual refresh of an existing finish.

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