Deck stain coverage depends on how thirsty the wood is: new smooth boards may take 250 ft² per gallon, while old weathered or rough-sawn wood can drink half as much. Most stains need two coats, applied thin. Railings and steps add a lot of surface, so include them.
How to use the Deck Stain Calculator
- Deck length
- Deck width
- Railing length
- Railing height
- Railing sides to stain
- Steps
- Step width
- Tread + riser
- Coats
- Coverage per gallon
- Price
Results update as you type, and every field accepts the units shown in its menu.
How it works
Enter the deck size, railing length and height, the number of steps and their size, the number of coats, the coverage on the label and the price per gallon.
Tips for an accurate estimate
- Take measurements at floor level and at the ceiling – walls and rooms are often slightly out of square.
- Use the manufacturer’s coverage, spacing and installation data when it differs from the typical values here.
- Keep a little extra of every finish material for touch-ups and repairs later.
- Check local building codes and permits before structural, electrical, plumbing or gas work.
Common mistakes to avoid
- Sizing heating or cooling equipment by area alone when insulation, windows and climate make a big difference.
- Buying too little paint, stain or flooring and ending up with mismatched batches.
- Overlooking the extra material for steps, railings, gables and trim.
Inputs explained
| Field | What to enter |
|---|---|
| Deck length | Units: ft, m, in, yd, cm |
| Deck width | Units: ft, m, in, yd, cm |
| Railing length | Units: ft, m, in, yd, cm |
| Railing height | Units: in, cm, mm, ft, m |
| Railing sides to stain | Choose one: Both sides, One side |
| Steps | A number |
| Step width | Units: ft, m, in, yd, cm |
| Tread + riser | Units: in, cm, mm, ft, m |
| Coats | A number |
| Coverage per gallon | Choose one: 175 ft²/gal (typical), 250 ft²/gal (new, smooth), 125 ft²/gal (old, rough), 10 m²/L |
| Price | Units: /US gal, /L |
What each result means
- Area to stain = [Deck length]×[Deck width] + [Railing length]×[Railing height]×[Railing sides to stain] + [Steps]×[Step width]×[Tread + riser]
- Stain needed = [Area to stain]×[Coats]÷[Coverage per gallon]
- 1-gallon cans = ceil([Stain needed]÷0.003785411784 – 0.000001)
- Cost = [1-gallon cans]×0.003785411784×[Price]
Example values
How the main result changes when Deck length changes and everything else stays at the example values above:
| Deck length (ft) | Stain needed (US gal) |
|---|---|
| 8 | 4.05 |
| 12 | 4.59 |
| 16 | 5.14 |
| 20 | 5.69 |
| 24 | 6.24 |
| 32 | 7.34 |
Formula
Area = deck L × W + railing length × height × sides + steps × width × (tread + riser)Gallons = area × coats ÷ coverageWorked example
Inputs — Deck length: 16 ft; Deck width: 12 ft; Railing length: 40 ft; Railing height: 36 in; Railing sides to stain: Both sides; Steps: 3; Step width: 4 ft; Tread + riser: 18 in; Coats: 2; Coverage per gallon: 175 ft²/gal (typical); Price: $40 /US gal.
Results — Area to stain = 450 ft²; Stain needed = 5.14 US gal; 1-gallon cans = 6; Cost = $240.00.
Frequently asked questions
How much does a gallon of deck stain cover?
150–300 ft² for the first coat on most decks, less on rough or weathered wood.
How many coats of deck stain?
Usually two thin coats for semi-transparent and solid stains; one coat for some penetrating oils.
Should I stain the railings?
Yes – include both sides of the railing and all balusters; they can add 30–50% to the area.
What formula does the Deck Stain Calculator use?
Area = deck L × W + railing length × height × sides + steps × width × (tread + riser).