Deck Stain Calculator
Gallons of stain or sealer for a deck, including railings and multiple coats.
Stain coverage figures on the can assume smooth, previously finished wood. A deck that has weathered for two seasons is closer to a sponge: the grain has opened up and the first coat disappears into it. That is why the same gallon that covered 250 sq ft last time barely reaches 180 this time.
Two thin coats always beat one heavy one. A thick single coat sits on the surface, skins over, and peels in sheets within a year. A thin first coat that soaks in, followed by a second that builds the film, is what actually protects the wood from UV and moisture cycling.
How this calculator works
Every field is editable and the result updates as you type — nothing is submitted anywhere, all the maths runs in your browser. That matters for a number you are about to spend money on: you can see exactly which input moved the answer, and by how much.
What this calculation assumes
Assumes smooth, previously coated decking at the coverage printed on the can. Weathered, rough-sawn or virgin pressure-treated wood absorbs far more, and the first coat on dry timber can use twice the predicted amount.
Treat the result as an order-of-magnitude check rather than a final quantity. Product packaging changes, regional labour rates vary by a factor of two, and no calculator has seen your actual site.
Frequently asked questions
How many square feet does a gallon of deck stain cover?
About 250 sq ft for a smooth, previously stained deck, dropping to 150 to 200 on rough or weathered wood. Semi-transparent stains penetrate deeper and cover less per gallon than solid-colour stains, which build a film on the surface.
How long should new wood dry before staining?
Four to eight weeks for pressure-treated lumber, until a splash of water soaks in rather than beading. Staining too early traps the moisture from the mill inside the wood and the finish fails from below. Test by sprinkling water on a board — if it beads, wait.
Transparent, semi-transparent or solid stain?
Transparent shows the grain and offers the least UV protection. Semi-transparent balances both and is the usual choice for a decent deck. Solid hides the grain entirely, lasts longest, and is the only practical option once a deck has been stained solid before.
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