The gallon on the shelf does not tell the whole story. The same can covers half the square feet on fresh pine that it does on a deck that has been outside for a few years. Before you buy, decide what wood you are actually coating.
Read the wood, not just the size
Walk onto the deck and look. Pale, sanded, pressure-treated boards with sharp edges are new. Gray, faded, fuzzy boards that have never been sealed are weathered. The new stuff drinks stain; the old stuff still drinks, but more slowly because the surface has already opened up.
New wood coverage
Fresh, unsealed treated pine soaks up about 200 sq ft per gallon on the first coat. That number sounds low, and it is, because the boards are thirsty. If you stain a brand-new deck the weekend it goes down, plan on two gallons per 400 sq ft and expect the first coat to vanish into the grain.
Weathered wood coverage
Once the boards have aged a season or two, a gallon stretches to about 350 sq ft. The surface is already open, but not as empty as new pine. A gray deck that was last stained three years ago sits right around that number.
Solid versus semi-transparent
Solid color stain hides grain and covers gray patches the way paint does, but it sits on top and can peel if the deck moves. Semi-transparent soaks in and shows the wood figure, so it looks natural but will not cover dark stains. Pick solid when the deck looks beat up; pick semi-transparent when you like the grain.
One coat or two
Old, dry decks almost always take two thin coats. The first sinks in and primes; the second builds the color. New decks often get one heavy coat, because the wood itself provides the base. Always follow the can, but budget two coats for anything gray.
The 10% buffer
Handrails, stair risers, and the edge laps where a brush starts and stops drink more than flat boards. Add about 10% to the gallon count for those edges, and buy everything from the same batch number so the color matches.
Worked example
A 192 sq ft deck on new pine, two coats, 10% buffer, lands near 2 gallons. On weathered wood the same deck would need roughly half that.
Deck Stain Calculator
New treated pine covers near 200 sq ft per gallon, while weathered gray wood stretches a gallon to about 350 sq ft, so wood age drives the buy.
How to use
- Measure the deck boards and stairs in square feet
- Pick the wood age, new or weathered
- Choose solid color or semi-transparent stain
- Set the number of coats, two is common for old wood
- Read the gallons to buy
Supported formats and limits
- New unsealed wood drinks about 200 sq ft per gallon
- Weathered, dried-out wood covers near 350 sq ft per gallon
- Add roughly 10% for edges, rail boards and touch-ups
Examples
A 192 sq ft new-wood deck at two coats lands near 2 gallons.Common errors
- Deck area must be a positive number of square feet
- Wood age must be selected before gallons are shown
Privacy and browser support
All calculations run locally in your browser. No deck measurements are uploaded.
FAQ
Why does new wood need so much more stain?
Fresh treated pine is porous and thirsty. A gallon only stretches to about 200 sq ft on it. Let it weather three to six months and it will cover closer to 350 sq ft per gallon.
One coat or two?
One coat is enough on sealed or recently stained wood. Dry, gray, weathered decks usually need two thin coats, because the first soaks in and the second builds color.
Solid color or semi-transparent?
Solid hides grain and covers gray weathering like paint, but it builds a film that can peel. Semi-transparent shows the grain and soaks in, so it looks natural but does not hide stains.
How much extra should I buy?
Add about 10% over the math for handrails, stair risers, and the first edge lap. Stain cans from the same batch match, so extra never goes to waste.
Can I stain wet wood?
No. Wait at least 48 hours after rain. Wet wood traps moisture under the film and the stain peels next season.
How often do I restain?
Every two to three years in full sun, and every four to five years in shade. Splash water on the boards; if it beads, wait. If it soaks in, it is time.