Deck Stain Calculator
A deck stain calculator divides deck area by about 250 sq ft per gallon per coat. A 20 × 15 ft deck is 300 sq ft, so one coat takes 1.2 gal; two take 2.4.
How much deck stain do I need?
A deck stain calculator divides the deck’s surface area by the coverage of one gallon. Gallons = (length × width) ÷ 250 sq ft per gallon, for one coat. A 20 × 15 ft deck is 300 square feet, so one coat takes 1.2 gallons. At $40 a gallon that is $48. Two coats double it to 2.4 gallons.
The 250 figure is a planning rate for smooth, sound wood. The label on your stain gives its own rate, and the wood itself has the final say. A thirsty, sun-bleached deck can drink nearly twice as much.
The formula in plain words
- Area = deck length × deck width, in square feet.
- Gallons per coat = area ÷ 250.
- Total gallons = gallons per coat × number of coats. Do this step yourself.
- Cost = gallons × price per gallon.
The calculator does not round up, because stain is sold in quarts, gallons, and 5 gallon pails. Round up to whatever containers you are buying.
Worked examples
- A 20 × 15 ft deck, one coat (calculator defaults)
- Area: 20 × 15 = 300 sq ft
- Gallons: 300 ÷ 250 = 1.20 gallons
- Cost: 1.2 × $40 = $48.00
- Buy: one gallon plus a quart, or two gallons
- A 16 × 12 ft deck with 40 ft of railing, two coats
- Deck floor: 16 × 12 = 192 sq ft → 192 ÷ 250 = 0.77 gal ($30.72)
- Railing, entered as 40 × 3 ft = 120 sq ft → 0.48 gal
- One coat: 0.77 + 0.48 = 1.25 gal
- Two coats: 1.25 × 2 = 2.50 gallons, so buy 3 gallons
Run the floor and the railing as two separate entries and add the gallons. The railing in this example adds almost two-thirds to the stain needed.
Gallons per coat at different coverage rates
| Deck area | 250 sq ft/gal (smooth) | 200 sq ft/gal | 150 sq ft/gal (rough or dry) |
|---|---|---|---|
| 100 sq ft | 0.40 | 0.50 | 0.67 |
| 192 sq ft | 0.77 | 0.96 | 1.28 |
| 300 sq ft | 1.20 | 1.50 | 2.00 |
| 400 sq ft | 1.60 | 2.00 | 2.67 |
| 500 sq ft | 2.00 | 2.50 | 3.33 |
| 750 sq ft | 3.00 | 3.75 | 5.00 |
To use a lower rate in the calculator, scale the area instead. At 150 sq ft per gallon, multiply your area by 250 ÷ 150 = 1.67 before entering it.
How to measure your deck
- Floor: measure length and width of the decking. For L-shapes, split into rectangles.
- Stairs: add each tread (width × depth) and each wood riser (width × height).
- Railings: length × height, per side you are staining.
- Board edges and ends: these soak up extra stain. The rounding up covers them on most decks.
- Do a test: stain one board and see how much of a quart it takes. Then scale up.
Common mistakes
- Staining a dirty or gray deck. Mill glaze, mildew, and gray fibers block stain. Clean and brighten first, then let the wood dry.
- Over-applying penetrating stain. Extra stain that does not soak in stays tacky and peels.
- Forgetting the second coat. Many products call for two. Budget for both before you start.
- Buying from different batches. Tints can vary between batches. Buy all of it at once, or mix cans together in a bucket.
Related deck tools
Building or reboarding first? The decking board calculator counts boards, and the deck calculator covers framing too. If boards are cracked or soft, price fixes with the deck repair cost calculator before staining. A wood fence takes stain the same way; see the fence stain calculator.
Frequently asked questions
How much deck area does one gallon of stain cover?
This calculator uses 250 sq ft per gallon for one coat on smooth, sound decking. The real figure is on your product's label, and it drops on rough, weathered, or very dry wood. At 250 sq ft per gallon, a 300 sq ft deck takes 1.2 gallons per coat.
Does rough or weathered wood need more stain?
Yes. Dry, gray, or rough-sawn boards soak stain in, so coverage can fall well below the label rate. At 150 sq ft per gallon, the same 300 sq ft deck needs 2 gallons per coat instead of 1.2. Brush a test board first and see how far a quart goes.
How many coats of stain does a deck need?
Follow the product label. Many penetrating stains go on in one or two thin coats, often wet-on-wet, while solid stains usually need two. Multiply the one-coat result by the number of coats: 1.2 gallons per coat becomes 2.4 gallons for two.
Should I include railings and stairs in my deck area?
Yes, if you are staining them. Add stairs as tread width × tread depth for each step, plus risers if they are wood. For railings, a simple starting point is railing length × height as a separate rectangle; spindles have many faces, so round up rather than down.
Why isn't waste added by default for deck stain?
Stain is not cut like boards, so there are no offcuts. The variables are wood condition and coat count, which you can handle directly by lowering the coverage assumption or multiplying by coats. Round up to whole gallons, and keep the leftover for touch-ups.
Estimates only. Verify quantities with your supplier before purchasing.