Deck stain calculator: how much stain do I need?
Measure the deck floor, the railings and the steps, then pick the wood condition. Weathered wood soaks up more stain, so a gallon covers less. Check the coverage on the can you buy.
- Railings and steps
- Wood condition
- Gallons and pails
Railings count both sides as if solid, which runs a little high for open balusters. Each step counts a 10-inch tread and a 7 3/4-inch riser.
Before you stain
How it works
Area = deck length × width, plus railing length × height × 2 for both sides, plus steps × width × 17.75 inches (a 10-inch tread and a 7 3/4-inch riser, the limits in the International Residential Code).
Gallons = area × coats ÷ coverage per gallon. Smooth or newer wood defaults to 300 square feet, the top of the first-coat range on Behr DECKplus semi-transparent stain (250 to 300). Weathered or rough wood defaults to 200, the low end of the 200 to 400 range Behr lists for porous wood.
Coats default to 2, since Behr and Olympic both call for two coats on their deck stains. A second coat usually goes further, so this runs a bit high.
What to buy rounds up to whole gallons, and every 5 gallons becomes a 5-gallon pail.
About this tool
Who it's for
For anyone staining or sealing a wood deck this season.
Example
You enterA 16x12 deck, 28 feet of 3-foot railing, 3 steps 4 feet wide, smooth wood, 2 coats
You getAbout 2.5 gallons, so buy 3.
What's different
- Counts railings and steps, not just the floor.
- Changes coverage for weathered wood.
- Uses your can's coverage if it is different.
Gotchas and tips
- Solid stains often cover more per gallon than clear or semi-transparent.
- Clean the deck and let it dry before staining.
- Buy one batch so the color matches.
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Built and maintained by the GrabTheHammer team, using published figures from manufacturers and agencies, listed below. Updated November 2026. Spot a problem? Tell us.
Deck stain questions
How much deck stain do I need for a 12x16 deck?
The floor alone is 192 square feet. Two coats at 300 square feet per gallon is about 1.3 gallons. Railings and steps can double that, so measure them too.
Why does old wood need more stain?
Weathered wood is rough and dry, so it soaks up more. Behr lists 200 to 400 square feet per gallon depending on how porous the wood is.
Do I need two coats?
Most deck stain labels call for two thin coats. The second coat usually goes further than the first.
Sources: Behr DECKplus semi-transparent: coverage and coats; Behr Premium solid color stain data sheet; Olympic Maximum data sheet.