Short answer: a 12 × 12 deck needs about 2 gallons of semi-transparent stain for two coats, a 12 × 16 deck about 2 gallons, and a 16 × 20 deck about 3 gallons. Add railings and the number climbs: a 12 × 16 deck with 40 feet of railing needs about 3 gallons.
Below is the simple formula, a chart for common deck sizes and stain types, and the details that make real-world numbers go up or down.
Get the exact gallons for your deck
Calculate the amount of stain needed for your deck project.
The Deck Stain Formula
- Deck floor area: length × width. A 12 × 16 deck is 192 sq ft.
- Add railings: about 2 sq ft per linear foot of railing (both sides of the balusters and rails). 40 ft of railing ≈ 80 sq ft.
- Multiply by coats: most stains call for two coats on bare or weathered wood.
- Divide by coverage from the can.
- Add about 10% for absorption and waste, then round up to whole gallons.
Example: (192 + 80) × 2 coats = 544 sq ft. At 250 sq ft per gallon, that's 2.2 gallons, plus 10% is about 2.4, so buy 3 gallons.
Coverage per gallon varies by product and by how thirsty your wood is. Our calculator uses typical planning figures of 200 sq ft/gal for transparent, 250 for semi-transparent and 300 for solid stain. Always check the coverage printed on your can and use that if it's different.
Deck Stain Chart by Deck Size
Floor only (no railings), two coats, 10% extra, rounded up to whole gallons. These match our deck stain calculator.
| Deck size | Area | Transparent | Semi-transparent | Solid |
|---|---|---|---|---|
| 10 × 10 | 100 sq ft | 2 gal | 1 gal | 1 gal |
| 10 × 12 | 120 sq ft | 2 gal | 2 gal | 1 gal |
| 12 × 12 | 144 sq ft | 2 gal | 2 gal | 2 gal |
| 12 × 16 | 192 sq ft | 3 gal | 2 gal | 2 gal |
| 16 × 16 | 256 sq ft | 3 gal | 3 gal | 2 gal |
| 16 × 20 | 320 sq ft | 4 gal | 3 gal | 3 gal |
| 20 × 20 | 400 sq ft | 5 gal | 4 gal | 3 gal |
Doing one coat of semi-transparent stain? A 12 × 16 deck needs about 1 gallon, and a 20 × 20 deck about 2 gallons.
Numbers that land just above a whole gallon round up a full gallon. If the chart says 2 gallons but your math is close to the line, buy a quart extra for touch-ups rather than a third gallon.
Don't Forget Railings, Stairs and Skirting
Railings are the part people underestimate. Every baluster has four sides, and the top and bottom rails get stained too.
- Railings: add roughly 2 sq ft per linear foot
- Stairs: treat each tread and riser as a small rectangle, or estimate about 10–15 sq ft per step for a typical 3–4 ft wide stair
- Skirting or lattice: measure the face and roughly double it if you're staining both sides
Transparent, Semi-Transparent or Solid?
| Stain type | Look | Typical lifespan* | Best for |
|---|---|---|---|
| Transparent / clear | Shows all the grain | Shortest; often 1–2 years | New or beautiful wood |
| Semi-transparent | Tinted, grain still shows | Middle; often 2–3 years | Most decks |
| Solid | Opaque, like paint | Longest; often 3–5 years | Older or mismatched boards |
*Lifespan depends heavily on sun, foot traffic and climate. Horizontal surfaces wear faster than railings.
Solid stain hides more and lasts longer, but it can peel like paint and is hard to switch away from later. If you're not sure, semi-transparent is the safe middle ground.
Things That Make You Need More Stain
- Rough or weathered wood soaks up more stain, especially on the first coat.
- Brand-new pressure-treated wood usually needs to dry out before staining; check the stain label for the wait time.
- Hot, windy days make stain dry too fast and go on heavier. Stain in mild weather, out of direct midday sun.
- Spraying uses more than rolling or padding because of overspray.
Clean and brighten the deck before staining. Stain sticks to clean wood, not to dirt and mildew, and you'll get more even color with less product.
How to Stain a Deck (So You Don't Waste Stain)
- Clean the deck with a deck cleaner or brightener and let it dry completely. Many stain labels call for 24–48 hours of dry weather first.
- Do a water test: sprinkle water on the boards. If it soaks in, the wood is ready for stain. If it beads up, old sealer is still there or the wood is too new.
- Test a hidden spot to check the color before committing.
- Work two or three boards at a time, along their full length. Stopping in the middle of a board leaves lap marks where wet stain meets dry.
- Back-brush any puddles so stain soaks in evenly instead of pooling.
- Apply the second coat the way the label says. Some products want it while the first is still damp ("wet on wet"), others after it dries.
- Do railings first, then the floor, so drips land on boards you haven't stained yet.
What Will the Stain Cost?
Deck stain commonly runs somewhere around $30 to $60 per gallon, depending on the brand and type. At that range, the 2 gallons for a 12 × 12 deck works out to roughly $60–$120, and the 3 gallons for a 16 × 20 deck to roughly $90–$180, before applicators and cleaner. Prices vary by store and region, so treat these as ballpark figures.
When to Restain
Do the same water test once a year. When water starts soaking into the boards instead of beading, the finish is wearing thin and it's time for a maintenance coat. A maintenance coat on clean, previously stained wood often needs less stain than the first application, so the one-coat numbers above are a good guide.
Tools for a Deck Stain Project
Shur-Line
Deck Stain Pad Applicator With Pole
- ✓Covers boards fast
- ✓Works stain into the grain
- ✓Saves your back
Various
Deck Cleaner and Brightener
- ✓Removes dirt and mildew
- ✓Helps stain absorb evenly
- ✓Use before staining
Various
Semi-Transparent Deck Stain, 1 Gallon
- ✓Shows the wood grain
- ✓Good balance of look and lifespan
- ✓Check coverage on the can
Wooster
Angled Stain Brush, 3 Inch
- ✓For railings and balusters
- ✓Gets into gaps
- ✓Holds plenty of stain
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The Bottom Line
- Formula: (deck area + 2 sq ft per foot of railing) × coats ÷ coverage, plus 10%.
- A 12 × 12 deck needs about 2 gallons of semi-transparent stain for two coats; a 16 × 20 deck about 3.
- Railings and stairs add more than you'd expect, so count them.
- Check the coverage on your specific can, and plug your measurements into the free deck stain calculator for an exact number.
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