Deck Stain Calculator
Deck size, railing and coats in. Gallons out, with the railing counted properly and a lower coverage rate for weathered boards.
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Railing counted at 3 sq ft per linear foot, which allows for both faces, the cap and the balusters.
Get the deck quotedCoverage, and why the can is optimistic
Most deck stains quote 250 to 350 square feet a gallon, and that figure assumes smooth timber that has been sealed before. Published coverage data puts rough sawn or weathered boards nearer 150 to 200, and bare new cedar or pine lower still, because dry open grain drinks the first coat.
This calculator uses 300 for smooth, 200 for rough or weathered and 150 for thirsty bare timber, then rounds up to whole gallons. Running out halfway across a deck leaves a lap mark you cannot sand out.
The railing is most of the surface
A 40 foot railing with balusters is roughly 120 square feet of surface once you count both faces, the cap rail and every spindle. Skip it and you underbuy by a third on a small deck.
Two coats, or one
A second coat uses less than the first because the timber is already sealed, but only on a semi-transparent or solid stain. Penetrating oils are applied to refusal, meaning you stop when the wood stops taking it, so a second coat on top of a saturated board just sits there sticky.
Replacing boards before you stain? The deck board calculator works out the count, and our deck building and repair page covers the work itself.
Common questions
How much stain do I need for a deck?
Add the deck area to the railing counted at about three square feet per linear foot, then divide by the coverage rate. Three hundred square feet a gallon on smooth boards, nearer 200 on rough or weathered timber.
Why does weathered wood need more stain?
Weathering opens the grain, so the surface absorbs two to three times what a sealed board takes. Bare new cedar and pine are porous for the same reason and can drop to 150 square feet a gallon.
How do I count the railing?
Three square feet per linear foot is a reasonable allowance for a standard 36 inch railing with balusters. That covers both faces, the top of the cap rail and the spindles, which together are more surface than people expect.
Do I need one coat or two?
Semi-transparent and solid stains usually look better with two, and the second coat uses roughly two thirds of the first. Penetrating oils are applied until the wood stops absorbing, so a second coat often is not needed at all.
Should I stain a brand new deck right away?
Not always. Pressure treated timber often arrives wet and needs weeks to dry before it will take stain, and the test is to sprinkle water on it. If it beads rather than soaking in, it is not ready.
Does stain stop a deck rotting?
It slows the water that causes rot, which helps. What it does not fix is a wet detail underneath, like a ledger flashed badly or a post sat in standing water, and those are what actually take decks down.
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