How to work out how much deck stain you need
Add up every surface the stain goes on, multiply by the number of coats, and divide by the stain's spread rate for your wood:
- Deck floor: length × width.
- Railings: length × height × 2.0 with balusters (each spindle has four faces), or × 0.6 for an open rail — the factors Sherwin-Williams' deck calculator uses.
- Stairs: steps × stair width × 1.56 ft (an 11-in tread of two 2×6 boards plus a 7¾-in riser).
- Fence: length × height × sides.
Worked example — a 12×16 deck with 44 ft of 3-ft balustered railing and 3 steps, 4 ft wide: 192 + 264 + 18.8 = 475 sq ft. Two coats of a semi-transparent stain at 200 sq ft per gallon: 475 × 2 ÷ 200 = 4.75 gallons, so buy 5 gal.
Stain for common deck sizes
| Project | Wood area | Two coats | Buy |
|---|---|---|---|
| 10×10 deck | 299 sq ft | 2.99 gal | 3 gal |
| 12×12 deck | 379 sq ft | 3.79 gal | 4 gal |
| 12×16 deck | 475 sq ft | 4.75 gal | 5 gal |
| 16×20 deck | 675 sq ft | 6.75 gal | 7 gal |
| 100 ft of 6 ft privacy fence | 1,200 sq ft | 12 gal | 12 gal |
Decks include railings on three sides and 3 steps; the fence is stained on both sides.
Coverage by stain
Stain coverage swings far more than paint: thin toners spread widely on new wood, while a thick resurfacer like Cabot DeckCorrect covers about 75 sq ft per gallon for its two required coats. Weathered, gray wood is thirsty, so we plan at the low end of each range; on new, smooth boards we use the middle.
| Stain | First coat (sq ft/gal) | Coats |
|---|---|---|
| Thompson's WaterSeal Clear Wood Sealer | 200–400 | One light coat only. |
| Behr Premium Semi-Transparent (No. 5077) | 300; 2nd coat 500 | Two coats required: first at 300 sq ft/gal, a thinner second at 500. |
| Olympic Elite Semi-Transparent | 250–350 | Two coats recommended for maximum durability. |
| Cabot Semi-Transparent Stain & Sealer (oil) | 200–650 | Apply 1 coat only. |
| Sherwin-Williams SuperDeck Semi-Transparent | 350 new / 200 weathered / 150 rough | Two coats may be necessary to reach the selected color. |
| Ready Seal Exterior Wood Stain & Sealer | 150 new / 150 weathered / 125 rough | The rate covers Ready Seal's full first application, including a wet-on-wet second pass where the wood takes it. New smooth wood may take only one pass. |
| Valspar One Coat Semi-Transparent | 150–400 | One coat. |
| Behr Premium Solid Color (No. 5011) | 200–400; 2nd coat 400–800 | Two thin coats: 200–400 sq ft/gal first, 400–800 second. |
| Sherwin-Williams WoodScapes Solid Color House Stain | 200–400 | 2 coats. |
| Cabot DeckCorrect resurfacer | 150; 2nd coat 150 | Requires two coats; 75 sq ft per gallon for both. |
One coat or two?
Follow the can. Many semi-transparent and toner stains are one-coat products, and a second coat that can't soak in stays on the surface and peels. Solid stains and some semi-transparents call for two thin coats — and the second often spreads further: Behr rates its semi-transparent at 300 sq ft per gallon for the first coat and 500 for the second.
Rough-sawn and weathered wood
Rough fence boards and old decks absorb far more stain. Ready Seal rates rough cedar at 125 sq ft per gallon against 150 for smooth, and Sherwin-Williams rates SuperDeck at 350 on smooth wood but 100–200 on rough or porous wood. New lumber needs time to dry first — Ready Seal asks for 12% moisture or less.
Common mistakes
- Counting only the deck floor. Balustered railings can take as much stain as the floor itself.
- Trusting a quick rule of thumb: Olympic's guide (1 gallon up to 175 sq ft, 2 gallons up to 550 sq ft, 3–4 gallons up to 700 sq ft) ignores coats and wood condition.
- Staining over dirt, mildew or failing old coatings — clean and, if needed, strip first.
- Staining in direct sun or before rain; check each product's minimum temperature.
Building the fence first? Use the fence calculator and the post hole concrete calculator. Painting the house next? Try the exterior paint calculator.