How to use the fence and deck stain calculator
Choose fence or deck. For a fence, enter the total length, the height and whether you’re staining one side or both, then the picket width and the gap between pickets (0 for a solid fence). For a deck, enter its length and width and add the railings and stairs as extra square feet.
Set the coats and the coverage per gallon from the can. Labels give a range: use the low end for rough-sawn, weathered or very dry wood, the high end for smooth new boards. Add the price per gallon to see the cost.
To count the posts, rails and pickets for a new fence, use the fence calculator; for deck boards and joists, the deck calculator.
The formula
- Fence area = length × height × sides × picket ÷ (picket + gap)
- Deck area = length × width + railings and stairs
- Gallons = area × coats ÷ coverage per gallon
We then suggest cans: whole gallons, plus quarts for the remainder. Three quarts cost about as much as a gallon, so we round those up. A remainder under 0.05 gallon is too small to buy a quart for.
Worked example: 100 ft of 6 ft fence, both sides
- 100 × 6 × 2 sides = 1,200 sq ft of fence face
- 5.5 in pickets with 1/4 in gaps: 1,200 × 5.5 ÷ 5.75 = 1,148 sq ft of wood
- One coat at 250 sq ft per gallon: 1,148 ÷ 250 = 4.59 gallons → buy 5 gallons
Worked example: 16 × 12 ft deck with 60 sq ft of railings, two coats
- 16 × 12 = 192 sq ft + 60 = 252 sq ft
- 252 × 2 coats ÷ 250 = 2.02 gallons → buy 2 gallons
Stain for a fence by size
Both sides, 5.5 in pickets with 1/4 in gaps, one coat at 250 sq ft per gallon.
| Fence | Area | Stain | Buy |
|---|---|---|---|
| 50 ft × 4 ft | 383 sq ft | 1.53 gal | 2 gallons |
| 100 ft × 4 ft | 765 sq ft | 3.06 gal | 3 gallons + 1 quart |
| 50 ft × 6 ft | 574 sq ft | 2.3 gal | 2 gallons + 2 quarts |
| 100 ft × 6 ft | 1,148 sq ft | 4.59 gal | 5 gallons |
| 150 ft × 6 ft | 1,722 sq ft | 6.89 gal | 7 gallons |
| 200 ft × 6 ft | 2,296 sq ft | 9.18 gal | 9 gallons + 1 quart |
| 300 ft × 6 ft | 3,443 sq ft | 13.77 gal | 14 gallons |
Stain for a deck by size
Deck floor only, at 250 sq ft per gallon. Add railings and stairs for your deck.
| Deck | Area | One coat | Two coats |
|---|---|---|---|
| 10 × 10 ft | 100 sq ft | 2 quarts | 1 gallon |
| 12 × 12 ft | 144 sq ft | 1 gallon | 1 gallon + 1 quart |
| 16 × 12 ft | 192 sq ft | 1 gallon | 2 gallons |
| 16 × 16 ft | 256 sq ft | 1 gallon | 2 gallons |
| 20 × 12 ft | 240 sq ft | 1 gallon | 2 gallons |
| 20 × 16 ft | 320 sq ft | 1 gallon + 2 quarts | 3 gallons |
| 24 × 16 ft | 384 sq ft | 2 gallons | 3 gallons + 1 quart |
Common mistakes
- Using the smooth-wood coverage on rough boards. By Cabot’s figures, rough-sawn wood takes about twice the stain of smooth wood. Start from the low end of the label’s range.
- Forgetting the back of the fence. Staining both sides doubles the stain, and the back has rails and posts that add more.
- Counting the deck floor only. Railings, balusters and stairs can add a lot of area. Measure them and add them in.
- Using the cans one after another. Cabot’s directions say to blend all the containers together when a job needs more than one, so the color stays even. Buy enough to finish in one go.
Frequently asked questions
How much stain do I need for a 100 ft fence?
About 4.6 gallons for a 6 ft fence stained on both sides, so buy 5 gallons. That assumes 5.5 in pickets with 1/4 in gaps, one coat and 250 sq ft per gallon. One side only takes about 2.3 gallons.
How many square feet does a gallon of stain cover?
Between 150 and 650 sq ft per coat, depending on the stain and the wood. Cabot Semi-Transparent covers 200–300 sq ft on rough wood and 450–650 on smooth; Thompson's WaterSeal Semi-Transparent lists 150–400. Use the figure on your can, and its low end for rough-sawn or weathered boards.
How much stain do I need for a 12 × 12 deck?
One coat over 144 sq ft is about 0.58 gallon at 250 sq ft per gallon, so buy 1 gallon. Two coats take about 1.15 gallons, or 1 gallon and a quart. Add the railings and stairs as extra square feet.
Do I need one coat of stain or two?
Follow the label. Cabot and Thompson's both recommend one coat of their semi-transparent stains. Some stains, especially on new or very porous wood, call for a second coat, so set the coats to match.
Do the gaps between pickets matter?
Yes, on spaced fences. The calculator stains only the picket faces, so 3.5 in pickets with 3.5 in gaps take half the stain of a solid fence. On a privacy fence with 1/4 in gaps the difference is about 4%.
Why does rough wood need more stain?
Rough-sawn and weathered boards have more surface and soak up more stain. Cabot lists 200–300 sq ft per gallon on rough wood against 450–650 on smooth, about half the coverage.
How do I count railings and stairs?
Work out each part's area (length × height, or length × width) and add up the square feet. For stairs, count each tread, plus the risers and stringers if you stain them. For railings, measure length × height on each side you stain and take off the gaps between balusters.
Sources
Formulas and defaults last reviewed October 30, 2026. How we check our math.