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Use this free stain calculator to figure out how much stain your deck or fence needs before you head to the store. Enter your measurements, pick your wood’s condition and the number of coats, and you’ll get the gallons to buy, rounded into 5-gallon pails and single gallons.
How much stain do you need?
Pick a deck or fence, enter your measurements in feet, and choose your wood’s condition.
Your project
Your wood and stain
Coverage varies by brand and by how thirsty your wood is. Check the label on your stain, and buy a little extra so you can finish in one session with the same batch.
| Project | Surface | Stain needed |
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Enter your own measurements above for a personal estimate.
How to Use the Stain Calculator
The stain calculator works in 3 easy steps:
- Pick deck or fence. For a deck, enter the length and width of the floor, plus any railing and steps. For a fence, enter the length, the height, and whether you’re staining one side or both.
- Choose your wood condition. Smooth, newer boards soak up the least stain. Weathered gray wood and rough-sawn fence pickets soak up much more.
- Choose coats and method. Two coats is the standard for most decks and fences. If you’re using a sprayer, the calculator adds 15 percent for overspray.
The result shows the total square feet, the gallons of stain you’ll need, and what to buy. Once you need 4 gallons or more, it rounds up to a 5-gallon pail, since a pail usually costs less than 4 or 5 single gallons.
Not sure of your deck size? Our square footage calculator handles L-shapes and odd layouts.
How Much Stain Do You Need per Square Foot?
It depends mostly on the wood. According to a Purdue University Extension guide written with the USDA Forest Products Laboratory, one gallon of penetrating stain usually covers about 300 to 400 square feet of smooth wood, but only 150 to 200 square feet of rough wood. Source: Purdue Extension — Selection and Application of Exterior Finishes for Wood
The stain calculator uses the low end of those ranges for the first coat, so you won’t come up short:
- Smooth, newer wood: about 300 square feet per gallon
- Weathered or older wood: about 200 square feet per gallon
- Rough-sawn wood: about 150 square feet per gallon
The second coat goes further because the wood is already partly filled. TWP, a deck stain maker, lists 150 to 200 square feet per gallon for a first coat and 200 to 300 for the second, so the calculator gives the second coat about 50 percent more coverage. Source: TWP — Deck Stain Calculator
One Coat or Two?
For rough-sawn or weathered wood, the Purdue guide recommends two coats, with the second coat brushed on before the first one dries. It says a single coat on new wood typically lasts 2 to 4 years, while a two-coat system on rough wood can last up to 10 years in some exposures. Source: Purdue Extension — Selection and Application of Exterior Finishes for Wood
Very new, dense wood is the exception. If the boards can’t soak up a second coat, it sits on the surface and gets sticky, so follow the directions on your stain’s label. We use Ready Seal exterior wood stain because it goes on without lap marks and doesn’t need a separate primer.
Brush, Roller, or Sprayer?
A brush or stain applicator pad works the stain into the wood and wastes very little. A battery-powered backpack sprayer is much faster on a long fence, but some stain always drifts away as overspray, so the stain calculator adds 15 percent when you pick the sprayer. Spray, then back-brush while it’s wet so it soaks in evenly. Our guide on how to stain a wood fence walks through each method.
How the Stain Calculator Measures Your Project
If you want to check the math yourself, here’s how each part is figured:
- Deck floor: length × width
- Railing: about 4 square feet per foot of railing, since you’re staining both sides plus the edges of every baluster
- Steps: each step counts as the stair width × 1.5 feet, for the tread and the riser
- Fence: length × height, times 2 if you’re staining both sides, plus 10 percent for the posts and rails on the back
Then the area is divided by the coverage for your wood, the second coat is added if you chose it, and the total is rounded up to the next tenth of a gallon. For a 16 × 12 deck of weathered wood with two coats, that’s 192 square feet and about 1.6 gallons.
Prep Before You Stain
Stain only soaks in as well as the wood lets it. Before you start:
- Clean the wood. Scrub off dirt, mildew, and old flaking stain with a floor scrub brush with a telescoping handle and a deck cleaner. Our guide on how to clean a wood deck covers each step.
- Let it dry. Give the wood at least 48 hours of dry weather after cleaning or rain.
- Check the forecast. Most stains need a dry day with no rain for 24 hours afterward. In central Indiana, fall stain jobs work best before nights drop near freezing.
Building a new fence first? Our fence calculator figures posts and concrete, and our board feet calculator helps you price the lumber.
Frequently Asked Questions About the Stain Calculator
How much stain do I need for a 12×12 deck?
A 12 × 12 deck is 144 square feet. With two coats on weathered wood, that’s about 1.2 gallons, so buy 2 gallons. Add your railing and steps in the stain calculator above for the full amount.
How much stain do I need for a 6 ft privacy fence?
Each 100 feet of 6-foot fence is 600 square feet per side. Two coats on weathered wood takes about 5 gallons for one side, or about 11 gallons for both sides once you add the posts and rails.
Does rough wood really need more stain?
Yes. Rough-sawn boards have more surface for the stain to soak into. The Purdue Extension guide puts rough wood at about half the coverage of smooth wood, 150 to 200 square feet per gallon instead of 300 to 400.
Should I buy extra stain?
Buy a little more than you need. Colors can vary slightly from batch to batch, so it’s best to finish the whole job with stain from the same purchase. Leftover stain is handy for touch-ups later.
Is a 5-gallon pail cheaper than single gallons?
Usually, yes. A 5-gallon pail typically costs less per gallon than buying single cans, which is why the stain calculator switches to a pail once you need 4 gallons or more.