What this calculator does
Enter the total square footage you plan to stain — floor, both faces of any railing, and posts if you are painting them — and the calculator returns the gallons of stain that area needs.
It runs at 8 gallons per 1,000 sq ft, which is two full coats at 250 sq ft per gallon per coat. That 250 figure is the conservative end of what manufacturers print: Cabot's Cabot Gold transparent wood finisher is rated 250–400 ft²/gal for one or two coats, so planning on the low end of the range means a shortage costs you a second trip to the store mid-project, while planning on the high end costs you an unopened gallon.
The rate box is editable on purpose. Your can's label always wins over anybody's table — including this one.
Count every surface, not just the floor
Most people measure the deck floor and forget the rest. A typical 12 × 16 ft deck with a 36-inch railing has 528 sq ft of stainable surface, not 192:
| Surface | How to measure it | 12 × 16 ft deck |
|---|---|---|
| Deck floor | Length × width, both in feet | 192 sq ft |
| Railing, both faces | Perimeter (2 × (L + W)) × railing height | 336 sq ft |
| Posts | Count each post face separately | add as needed |
| Underside and joists | Only if you stain before decking | add as needed |
On that deck the railing alone is 336 sq ft — 64% more surface than the floor you measured. Stain the underside and joists before the boards go down if you are building new: it is nearly free at that stage and impossible afterwards. If you are re-staining an existing deck, the underside is usually unreachable and does not count, but the wood is older and drinks more.
The second coat is not a second full coat
Naive math multiplies your area by two and divides by the label rate. Real math does not, and on a typical deck the difference is a whole gallon.
The first coat soaks into open fibre and fills it. The second coat lands on a surface that is already partly filled, so it spreads further. Behr Premium Semi-Transparent Stain & Sealer No. 5077 states this on its own data sheet: 300 ft²/gal for the first coat, 500 ft²/gal for the second. On a 528 sq ft deck that is the difference between 4.22 gallons (naive) and 3.52 gallons (coat one at 250 ft²/gal, coat two at 375 ft²/gal) — and because you buy in whole cans, 5 cans versus 4.
This calculator uses the conservative single-rate figure on purpose. A number that errs toward too much stain costs you one unopened gallon; a number that errs toward too little costs you a second trip with the gun and the boards open.
Wood condition moves the answer more than the label does
Coverage ratings assume new, smooth, planed wood. Three common conditions break that:
- Gray, weathered boards — ultraviolet light breaks down lignin in the surface cells and the fibres open, so the wood drinks roughly 30% more. That same 528 sq ft deck needs 5.49 gallons of coverage instead of 4.22, and with the usual 10% allowance for end grain, gaps and spills that is 7 cans instead of 5 — about two extra gallons, roughly $116 in product.
- Rough-sawn and textured boards — mill texture and saw marks multiply the surface the stain has to wet. Smooth planed lumber runs 300–400 sq ft/gal; rough texture drops toward 150–200.
- Dense hardwood decks — ipe and comparable tropical hardwoods are so dense that most stains barely penetrate and coverage can exceed 350 sq ft/gal. Those boards also need a hardwood formula or the finish will never dry.
Pressure-treated pine, the most common deck material, is the thirstiest of the common softwoods — plan on the low end of any label range.
Which product you buy changes the number by 5×
Coverage is a property of the product, not of your deck. The three families behave very differently:
| Stain type | Coverage per gallon | Coats | Gallons per 1,000 sq ft |
|---|---|---|---|
| Transparent or toner | 250–400 sq ft | 1–2 | 2.5–8 |
| Semi-transparent | 225–300 sq ft | 2 | 6.7–8.9 |
| Solid colour, film-forming | 75–200 sq ft | 2 | 10–26.7 |
Cabot's own product pages make the spread concrete: Cabot Gold transparent wood finishing is listed at 250–400 ft²/gal with one or two coats recommended, while DeckCorrect solid stain is listed at 75 ft²/gal with two coats and a four-to-six-hour dry time. On the 528 sq ft deck above, two coats of Cabot Gold at the top of its range needs 2.64 gallons; the same two coats of DeckCorrect needs 14.1 gallons — 5.3 times as much. A solid stain is not a slightly different product; it is a different quantity of material, and buying DeckCorrect while planning on Gold's coverage means running out on a third of the deck.
Read the coat count on the label rather than assuming two. Cabot Gold is rated for one or two coats; a penetrating oil such as Cabot Australian Timber Oil is a single-coat product, and a second coat on a horizontal surface can stay tacky or turn glossy.
Spraying costs you more product than brushing
Application method changes the amount you buy. Brush waste runs about 5%, roller about 10%, and a sprayer loses roughly 25% to overspray and to the gaps between deck boards. On 528 sq ft that is the difference between 5 cans brushed and 6 cans sprayed.
Spray rails and lattice, then back-brush every board immediately. A sprayer on its own lays product on top of the wood instead of into it, and a deck that looks even while still wet will dry patchy.
Worked examples
Example 1 — a 12 × 16 ft deck with a 36-inch railing, new pressure-treated pine, two coats, brushed.
Floor 12 × 16 = 192 sq ft. Railing perimeter 2 × (12 + 16) = 56 ft, at 3 ft high, both faces = 336 sq ft. Total stainable surface = 528 sq ft. The calculator returns 528 ÷ 1,000 × 8 = 4.22 gallons. Add the usual 10% for end grain, gaps and spills → 4.65 gallons, so buy 5 one-gallon cans. If you are spraying, that same deck takes 6 cans.
Example 2 — the same deck, one year old and already grey.
Same 528 sq ft, but grey wood drinks about 30% more: 4.22 × 1.3 = 5.49 gallons of coverage, plus 10% for gaps and spills = 6.04 gallons, so buy 7 cans against the 5 of Example 1. The extra two gallons are not waste; they are the price of grey wood.
Example 3 — a 20 × 20 ft deck with a 4 ft railing and eight posts, two coats, sprayed.
Floor 20 × 20 = 400 sq ft. Railing perimeter 80 ft at 4 ft, both faces = 640 sq ft. Eight 6-inch posts at 4 ft = 16 sq ft. Total = 1,056 sq ft. The calculator returns 8.45 gallons; with 10% for gaps and spills that is 9.29 gallons, and spraying adds 25% → 11.62 gallons, so buy 12 one-gallon cans. Brushed instead of sprayed, the same deck needs 10.
Two light coats beat one heavy coat
Heavy coats stay tacky and attract dirt, and they do not penetrate. Two thin coats applied wet-on-wet — the second while the first is still wet — let the second coat bond into the first instead of sitting on it. Stain both faces of a fence the same day for the same reason: sealing one face and not the other traps moisture inside the board and warps it.
Stain in the shade on a cool overcast day if you can. Boards in direct sun flash off the solvent before the stain can spread, so you lay it on heavier to get the same look and use more product for the same result.
Pair it with the rest of the deck job
The same deck dimensions feed the other calculators on this site, and running them together avoids a second trip to the lumber yard. The deck board calculator turns the same 12 × 16 ft footprint into a board count and linear feet, so you can price decking and stain in one sitting. If you are laying a paver pad or a gravel base underneath, the paver base calculator and the gravel driveway calculator cover the sub-base, and the fence calculator sizes the railing posts that feed the surface area above.
Sources and standards
Where these figures come from
Coverage rates, coat counts and dry times below are taken from the manufacturers' own published product data. Where a value depends on your product and your wood, the calculator takes the conservative end of the range rather than the best case.
- Cabot Gold Wood Finishing — transparent, 250–400 ft²/gal, one or two coats, recoat after 24 hours.
- Cabot DeckCorrect Wood Stain — solid colour, 75 ft²/gal, two coats, 4–6 hour dry and recoat.
- Cabot How-To Guide for Wood Stain — surface preparation, application and recoat guidance.
- Cabot Wood Stain Project Calculator — the manufacturer's own project sizing tool.
- Sanderscore Deck Stain Calculator — independent coverage tables compiled from Behr, Cabot, Olympic, Thompson's and Ready Seal data sheets, including the first-coat/second-coat rate difference.
Figures, formulas and reference tables last verified: 26 October 2026.