Deck Stain Calculator
To stain a 20 × 15 ft deck with 2 coats you need about 330 sq ft of coverage (with 10% waste) — 3 gallons, based on 250 sq ft of coverage per gallon per coat on smooth wood.
Reviewed by The ponderloop teamUpdated 2026-07-11How we calculate
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0 sq ft + 0% waste = 0 sq ft
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How this number is calculated
0 sq ft (no waste added) ÷ 125 sq ft per gallon = 0 gallons
Shopping list
- Semi-transparent deck stain
- Stain applicator pad
- Deck cleaning brush
- Paint tray for stain
- Deck wood cleaner/brightener
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Methodology & assumptions
Deck area is deck length times deck width, using this tool's inputs directly. That area is divided by coverage per gallon per coat — a 250 sq ft/gal baseline for smooth, relatively new wood, divided by your number of coats — then multiplied by your chosen waste percentage and rounded up to the next whole gallon. Rough-sawn or weathered decking absorbs more and can cover well below this baseline.
- Manufacturer coverage specs (~250 sq ft/gal per coat, semi-transparent deck stain on smooth wood)
- Typical US deck stain retail price range, 2026
Worked examples
| Room | Result |
|---|---|
| 20 × 15 ft deck, 2 coats, +10% waste | 300 sq ft + 10% waste ≈ 330 sq ft → 3 gallons |
| 12 × 12 ft deck, 1 coat, exact | 144 sq ft, no waste → 1 gallon |
| 30 × 20 ft deck, 2 coats, +10% waste | 600 sq ft + 10% waste ≈ 660 sq ft → 6 gallons |
Frequently asked questions
- How many gallons of deck stain do I need?
- Multiply the deck length by width in feet to get the square footage, then add 10% for touch-ups if you want a buffer. Divide by the coverage per gallon per coat (about 250 sq ft for smooth wood) divided by your number of coats, and round up to the next whole gallon.
- Why might my deck use more stain than the 250 sq ft/gal estimate?
- The 250 sq ft/gal figure assumes relatively smooth, newer wood. Rough-sawn lumber, weathered or grayed decking, and previously-stripped or sanded wood are much more porous and soak up stain faster — real coverage on those surfaces can drop to 100-150 sq ft per gallon, roughly half the smooth-wood baseline. If your deck is old, rough, or has never been sealed, plan on buying extra.
- How many coats of deck stain do I need?
- Two coats is standard for most deck stains and is this calculator's default — it gives better UV and water protection and more even color. Some solid-color stains are rated for one coat; always check the product label, since formulations vary.
- Does the number of coats change how much stain I need?
- Yes, directly — coverage per gallon is divided by the number of coats, since a second coat needs its own full pass over the same area. Two coats roughly doubles the gallons versus one coat for the same deck size.
- Should I round up or down when figuring out how many gallons to buy?
- Always round up to the next full gallon. Stain is mixed in batches, and running short partway through a deck can leave a visible line where you resume, especially with semi-transparent products.