Deck Stain Calculator
How much stain or sealer your deck needs, counting the floor, both sides of the railings and the stairs, for rough or smooth wood and one or two coats.
Gallons = square feet ÷ coverage. Semi-transparent stain covers about 150–250 sq ft per gallon (less on rough, weathered wood); solid stain 200–300. A 16 × 12 ft deck with 40 ft of railing and four steps is about 365 sq ft: about 3–4 gallons for two coats of semi-transparent stain on weathered wood.
Stain coverage per gallon
| Product | Rough or weathered | Smooth | Second coat |
|---|---|---|---|
| Semi-transparent stain | 150 sq ft | 250 sq ft | ~50% (wet-on-wet) |
| Solid stain | 200 sq ft | 300 sq ft | Same as first |
| Clear sealer or toner | 200 sq ft | 300 sq ft | ~50% (wet-on-wet) |
| Exterior paint | 250 sq ft | 350 sq ft | Same as first |
Stain like a pro
- Clean and brighten, then let the wood dry for 24–48 hours.
- Do a water test: if drops soak in, the wood is ready for stain.
- Stain two or three boards at a time along their full length to avoid lap marks.
Frequently asked questions
How much stain do I need for my deck?
Measure the floor (length × width), add both sides of the railings (length × height) and the stairs, then divide by the stain's coverage: about 150–250 sq ft per gallon for semi-transparent on weathered wood. Multiply for the number of coats.
How many gallons of stain for a 12 × 12 deck?
The floor alone is about 160 sq ft with board edges, so roughly 1–1.5 gallons per coat of semi-transparent stain on weathered wood, more with railings and stairs.
How many coats of deck stain do I need?
Most semi-transparent stains go on in one or two thin coats, the second applied wet-on-wet; solid stains usually need two full coats. Follow the label.
Why does rough wood use more stain?
Rough-sawn and weathered wood is porous and soaks up more stain, so a gallon covers less area than on smooth or previously stained wood.
Should I stain the deck railings too?
Yes, usually with the same stain. Railings with balusters have a lot of surface: count about their length × height for both sides.
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Coverage ranges reflect typical manufacturer label figures for each product type; your can's label takes priority. Board edges add 10% to the floor; railings count length × height for both sides of rails and balusters; stairs about 2 sq ft per foot of width per step. Penetrating stains' second coat is estimated at half the first.