Fence Stain Calculator

How much stain a fence needs

Fence stain is sold by the gallon, and the number of gallons comes from one piece of arithmetic: total surface area divided by coverage per gallon. The calculator above runs it in this order:

• Area per side = fence length × fence height. A 150-foot run of 6-foot fence is 900 square feet of face.
• Multiply by sides. Stain both sides and that 900 becomes 1,800 square feet.
• Multiply by coats. Two coats on 1,800 square feet is 3,600 square feet of actual coating.
• Add a waste allowance. Brushes, rollers, drips and touch-ups eat about 10% on a normal job.
• Divide by coverage. A gallon of semi-transparent stain covers roughly 250 square feet on smooth wood, so 3,960 ÷ 250 = 15.84 gallons.

Then you round up, because stain is not sold in fractions of a gallon, 16 gallons. That rounding step is why the calculator shows both the exact figure and the number to buy. Rounding up is not waste: leftover stain from the same batch is what you will use for touch-ups after the first winter.

Worked example: 150 feet of 6-foot fence, both sides, two coats

Take a typical backyard privacy fence: 150 feet long, 6 feet tall, both sides stained, two coats of a semi-transparent stain rated at 250 square feet per gallon, with a 10% waste allowance.

• One side: 150 × 6 = 900 sq ft
• Both sides: 900 × 2 = 1,800 sq ft
• Two coats: 1,800 × 2 = 3,600 sq ft
• With 10% waste: 3,600 × 1.10 = 3,960 sq ft
• Gallons: 3,960 ÷ 250 = 15.84, so buy 16 gallons

At $45 a gallon that is $720 in stain, or about 18 cents for every square foot of fence face. Now change one variable at a time. Stain only the side that faces the street and you are at 1,980 square feet, 7.92 gallons, 8 gallons to buy, $360. Drop the coverage figure to 200 square feet per gallon because the fence is 12-year-old rough cedar and the same job needs 3,960 ÷ 200 = 19.8, so 20 gallons and $900.

That gap between "a fence" and "your fence" is more than double, and it is the reason a one-coat guess usually ends in a second trip to the store. Stain does not keep well once the can is opened, so buying the right amount the first time matters more than buying cheap.

Why your fence usually drinks more stain than the label says

Coverage figures are measured on smooth, planed, kiln-dried lumber. Fences are rarely that. Each of these pushes your real number up:

• Rough-sawn or weathered boards soak up 30 to 50% more stain than smooth wood. This is the single biggest factor on most jobs.
• New cedar and redwood are open-grained and thirsty, they can take a third more than a pine board of the same size.
• Picket and board-on-board fences have twice the edges and more end grain, which absorbs faster than a flat face. Add 10 to 15%.
• Spraying without back-brushing loses 10 to 30% to overspray and wind, and what lands is a thinner film that fails sooner.
• End grain on post tops and rail ends acts like a sponge and needs a second pass.
• The second coat takes less than the first, usually 60 to 70% of it, because the wood is already sealed.

The calculator treats the second coat as a full coat, which is the safe direction to be wrong in. If you are undecided between one coat and two, buy the one-coat amount plus one spare gallon, apply the first coat, and measure what is left before you commit.

Fence stain coverage at a glance

Coverage varies far more by product than by brand. These are realistic ranges for a single coat on a smooth fence in good condition:

Two patterns are worth remembering. First, the products that last longest cover the most area per gallon, a solid color stain on our 3,960-square-foot example needs only 10 gallons against 16 for a semi-transparent, and it will not need recoating for years. Second, clear sealers are the cheapest per gallon and the most expensive per year, because you are back out there every other spring. The Ohio State University Extension publishes plain-language guidance on how different wood finishes behave outdoors if you want to go deeper.

Buying stain without wasting money

Two habits separate a $700 job from a $900 one. First, compare price per square foot, not price per gallon. A $30 gallon rated at 150 square feet costs you 20 cents per square foot; a $45 gallon rated at 250 square feet costs 18 cents. The cheaper can is the more expensive job.

Second, buy the amount the calculator gives you, in the largest container that fits. On the 16-gallon example, three 5-gallon pails plus one single gallon is usually cheaper than sixteen singles and gives you a spare gallon for touch-ups. Keep the batch or lot number from the label and write it on the underside of a rail, if you need to match a repair panel in three years, that number is the only way to get an identical color.

• One 5-gallon pail covers about 1,250 sq ft at 250 sq ft per gallon.
• Buy one spare gallon, not one spare pail. Opened stain skins over in a year or two.
• If two amounts are close, buy the smaller one plus a quart and check coverage after coat one.
• Store leftovers upside down and indoors; freezing ruins most water-based stains.

Getting the coverage the label promises

Coverage claims assume the wood is ready and the weather cooperates. Get those two right and your estimate will hold within a gallon or two:

• Temperature: air and wood between 50°F and 80°F. Below 50°F the film stops curing; above 90°F the stain flashes off before it soaks in.
• Weather: no rain for 24 to 48 hours. Check the National Weather Service forecast before you open a can, one surprise shower means redoing the whole run.
• Moisture: wood under 15% on a moisture meter. Wet boards push the stain back out and you lose coverage.
• Preparation: clean, dry, dull surface. Gloss and mildew both block absorption.
• Application: two thin coats beat one thick one. Back-brush every sprayed section while it is still wet.
• Mixing: stir, never shake, so you do not whip air bubbles into the film.

If you want to reduce the solvent load in your backyard, the EPA Safer Choice program lists products that meet a lower-toxicity standard, and water-based stains in general are easier to clean up and safe around plants once dry. Whichever you pick, the gallons are the same arithmetic, which is what the calculator above is for.