Deck Stain Calculator — Stain & Sealer Quantity
Enter your deck area, coats, product type, and wood condition to get a purchase-ready gallon and quart count.
Stain Needed
3 gal 3 qt
3.66 gal exact · 320 sq ft × 2 coats ÷ 175 sq ft/gal
Coverage Rate Used
175 sq ft/gal
Semi-transparent stain, new/smooth wood, per coat
How much deck stain you actually need
Stain and sealer coverage isn't a fixed number — it depends on the product and the wood. Clear sealers sit closest to the surface and cover the most area; semi-transparent stains penetrate deeper and cover less; solid (opaque) stains behave more like exterior paint. On top of that, weathered, gray, or rough-sawn wood is far more porous than new lumber and can soak up 39-50% more product for the same square footage.
This calculator multiplies your total surface area by the number of coats, divides by the coverage rate for your product and wood condition, and rounds the result up to the nearest quart — because stain is sold in gallon and quart containers, not by the fluid ounce.
Coverage rates by product and wood condition
Approximate square feet covered per gallon, per coat. These are aggregated planning estimates drawn from general deck-stain buying-guide coverage ranges (linked below) — not a "midpoint" of any single manufacturer's product data sheet. Real products vary far more than a two-condition table can capture: BEHR's DECKplus semi-transparent stain data sheet lists 250-300 sq ft/gal for a first coat (500-600 for a second coat), while Cabot's semi-transparent stain + sealer lists 200-650 sq ft/gal. Treat the table below as a conservative starting estimate, and always check your specific product's own data sheet — especially if your total lands close to a gallon or quart boundary.
| Product Type | New / Smooth Wood | Weathered / Rough Wood |
|---|---|---|
| Clear sealer | 300 sq ft/gal | 200 sq ft/gal |
| Semi-transparent stain | 175 sq ft/gal | 125 sq ft/gal |
| Solid (opaque) stain | 250 sq ft/gal | 180 sq ft/gal |
Sources: DeckStainHelp.com — How Much Deck Stain Should I Buy? · DeckStainHelp.com — Deck Stain Calculator · FramingCalc — Stain Coverage Calculator.
Worked example
- Total area: 320 sq ft deck + 0 railing + 0 stairs = 320 sq ft.
- Coverage needed: 320 sq ft × 2 coats = 640 sq ft of coverage.
- Gallons: 640 ÷ 175 sq ft/gal (semi-transparent, smooth) = 3.66 gal.
- Round up to a buyable amount: 3.66 gal rounds up to 3 gal 3 qt — the next full quart above the exact amount.
Always round up rather than down. Running short mid-coat means a second trip to the store and a visible lap mark where you stopped.
Frequently asked questions
- How many gallons of stain do I need for a 300 sq ft deck?
- For two coats of semi-transparent stain on smooth wood (175 sq ft/gal coverage), a 300 sq ft deck needs 300 × 2 = 600 sq ft of coverage ÷ 175 sq ft/gal = 3.43 gallons, which rounds up to 3 gal 2 qt. Solid stain or clear sealer will need different amounts because their coverage rates differ.
- Why does weathered wood need more stain than new wood?
- Weathered, gray, or rough-sawn wood has an open, porous surface that soaks up far more liquid than smooth new lumber. Across the coverage table above, that runs 125-200 sq ft per gallon on weathered wood versus 175-300 sq ft per gallon on smooth new wood, depending on the product — roughly 39-50% more product for the same area.
- Does a second coat use as much stain as the first?
- No — the first coat gets absorbed into open wood grain, while the second coat mostly sits on an already-sealed surface, so it goes further in practice. This calculator uses a straightforward area × coats formula, which is intentionally conservative, so leftover product on a two-coat job is normal and worth keeping for touch-ups.
- Should I include railings and stairs in my deck stain estimate?
- Yes if you're staining them in the same session — vertical baluster and stair surfaces add real square footage even though they look small. A rough rule of thumb is 1.5-2 sq ft of surface per linear foot of railing (both faces of the balusters and top/bottom rails) and the actual tread + riser area for stairs.