Deck Stain Calculator + How to Stain a Deck, Step by Step
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Enter your deck's floor, railings, stairs and any fence below, and the calculator returns the gallons (or litres) of stain to buy and what it will cost, using coverage rates that match your product and the condition of the wood. Below it: a chart for common deck sizes, and a step-by-step guide to staining a deck so the stain actually lasts.
How the calculator works
Deck stain runs about $30-$60 a gallon, and both mistakes cost you: buy too little and the mid-job store run leaves a lap mark where the wet edge dried; buy too much and the leftovers skin over in the garage. The calculator adds up the surfaces people actually stain (the floor, the railings, the stairs and any fence), then divides by a coverage rate that matches your product and your wood instead of the label's best case.
Railings are the classic estimating miss. A 36-inch railing with balusters has stainable surface on both sides, top and bottom rails, and every baluster face. It works out to roughly 3.5 square feet per linear foot of railing, so 28 feet of railing is nearly 100 extra square feet, half a deck floor's worth on a small deck.
The formulas:
Total area = (Length × Width) + (Railing ft × 3.5) + (Steps × Stair width × 1.5) + (Fence length × Height × Sides)
First coat = Total area ÷ Coverage rate
Second coat = First coat × 0.67 (a second coat goes onto wood that's already partly sealed, so it goes about a third further)
Buy = (First + Second) × 1.10, rounded up to whole gallons
Typical real-world coverage per gallon (first coat):
| Product | New / smooth wood | Weathered / rough wood |
|---|---|---|
| Penetrating oil-based stain | ~175 sq ft | ~125 sq ft |
| Water-based semi-transparent | ~250 sq ft | ~150 sq ft |
| Solid-color stain | ~300 sq ft | ~200 sq ft |
| Deck / porch paint | ~300 sq ft | ~200 sq ft |
If your can states a rate, type it into the coverage field. The presets are field-realistic averages; the label knows its own formula, but its upper figure assumes smooth new wood.
How much stain for common deck sizes
Deck floor only, one coat, with the 10% margin, rounded up to whole gallons. Add railings, stairs and a second coat with the calculator above.
| Deck size | Floor area | Oil stain, new wood | Oil stain, weathered | Water-based, 2 coats, weathered |
|---|---|---|---|---|
| 10 × 10 ft | 100 sq ft | 1 gal | 1 gal | 2 gal |
| 12 × 12 ft | 144 sq ft | 1 gal | 2 gal | 2 gal |
| 10 × 16 ft | 160 sq ft | 2 gal | 2 gal | 2 gal |
| 12 × 16 ft | 192 sq ft | 2 gal | 2 gal | 3 gal |
| 12 × 20 ft | 240 sq ft | 2 gal | 3 gal | 3 gal |
| 16 × 16 ft | 256 sq ft | 2 gal | 3 gal | 4 gal |
| 16 × 20 ft | 320 sq ft | 3 gal | 3 gal | 4 gal |
| 20 × 20 ft | 400 sq ft | 3 gal | 4 gal | 5 gal |
For anything over about 4 gallons, a 5-gallon pail is usually cheaper per gallon than single cans, and it keeps the color identical across the whole deck.
Worked example
A 12 × 16 ft deck with 28 feet of railing and 3 steps 3 ft wide, weathered pressure-treated pine, getting a penetrating oil stain:
Area = (16 × 12) + (28 × 3.5) + (3 × 3 × 1.5) = 192 + 98 + 13.5 = 303.5 sq ft
First coat = 303.5 ÷ 125 = 2.4 gallons; with the 10% margin, buy 3 gallons.
Those railings turned a "two-gallon deck" into a three-gallon order, exactly the miss that sends people back to the store with a wet edge drying behind them.
How to stain a deck, step by step
Most deck stain failures (peeling, blotchy color, stain that's gone in a year) come from prep, not from the stain. Plan on two days: one to clean, then at least a day or two of drying before you stain.
1. Check the weather. You want a dry spell: no rain for 24-48 hours after staining, temperatures roughly between 50°F and 90°F (10-32°C), and ideally an overcast day or a time when the deck is in shade. Stain applied in hot, direct sun flashes off before it can soak in.
2. Clear the deck and protect what's around it. Move furniture and planters, sweep, and cover plants, siding and the house wall below the deck with plastic or drop cloths.
3. Strip old film finishes if they're peeling. A penetrating stain can't soak through old paint or a peeling solid or acrylic stain. If the old finish is flaking, it has to come off first; see our paint remover for wood decks guide, or sand it back (our sanders for exterior paint removal guide covers the tools). A faded old oil stain doesn't need stripping; cleaning is enough.
4. Clean the wood. Mix an oxygen-based deck cleaner with water, wet the deck, apply the cleaner with a pump sprayer or a mop, let it work for the time on the label, then scrub with a stiff brush and rinse well. Avoid chlorine bleach: it kills mildew on the surface but damages the wood fibers and doesn't remove dirt.
5. Brighten the wood (recommended). A wood brightener goes on after the cleaner, while the wood is still wet. It neutralizes the cleaner, removes the grey look and tannin stains, and opens the grain so the stain absorbs evenly. Rinse again.
6. Let it dry completely. Give it at least 24-48 hours of dry weather. Then do the water test: sprinkle a little water on the boards. If it soaks in within a minute or so, the wood is ready. If it beads up, wait longer. New pressure-treated wood usually needs a few weeks to a few months before it passes.
7. Sand only where needed. Knock down raised grain, splinters and fuzzy spots with 60-80 grit on a pole sander or random orbital sander. Don't sand the whole deck smooth: very smooth boards absorb less stain. Sweep or blow off all the dust.
8. Stir the stain and test it. Stir well (don't shake) and mix several cans together in a bucket if you bought more than one, so the color matches everywhere. Try it on a hidden board first; most stains look darker wet than dry, and some, like Ready Seal, take a couple of weeks to settle to their final color.
9. Stain the railings first, then the floor. Do railings, balusters and posts before the floor, so drips land on unstained boards and get covered. Then stain the floor 2-3 boards at a time, along their full length, keeping a wet edge. Stopping in the middle of a board is what leaves lap marks. Plan the floor so you finish at the stairs, not in a corner.
10. Back-brush if you spray or roll. A pump sprayer or roller is fast, but work the stain into the wood with a stain brush right after, so it gets into the grain and doesn't pool. For a penetrating oil, wipe or brush out any stain still sitting on the surface after the time on the can (often 20-30 minutes); oil that can't soak in stays sticky.
11. Second coat, if your stain needs one. Most penetrating oils are one coat (or two passes wet-on-wet, following the can). Water-based and solid stains usually need two thin coats, with the drying time on the can between them.
12. Let it cure before using the deck. Light foot traffic is usually fine after 24-48 hours, furniture after 48-72 hours. Our deck stain drying time guide covers the details by stain type and weather.
What you'll need
Besides the stain itself (our oil-based deck stain guide ranks the ones worth buying), these are the tools and prep products that make the job faster and the result last longer. We earn a small commission from the Amazon links below, at no extra cost to you - see our affiliate disclosure.
- DEFY Wood Deck Cleaner (2 lb powdered concentrate) - an oxygen-based cleaner you mix with water. It lifts grey, dirt and mildew without the fiber damage of bleach, and one container is enough for a typical deck.
- DEFY Wood Brightener (1 gallon) - the second step after cleaning: it neutralizes the cleaner, brightens greyed wood and helps the stain absorb evenly. The Restore-A-Deck Cleaner and Brightener are a good alternative pair.
- Chapin 25020 Clean 'N Seal Deck Sprayer (2 gallon) - a pump sprayer made for deck cleaners and transparent stains and sealers, with fan nozzles. Use it to apply the cleaner and brightener, and to lay down transparent stain fast before back-brushing.
- Wooster Bravo Stainer Brush (5-1/2 in) - a wide stain brush with a threaded handle that takes an extension pole, so you can back-brush the floor standing up. Works with oil and water-based stains.
- Shur-Line Deck Stain Pad with Groove Tool - a pad on a pole for the floor boards, plus a groove tool that gets stain into the gaps between boards. Faster and neater than a brush on large, flat areas.
Frequently Asked Questions
How much stain do I need for a 12x12 deck?
The floor alone is 144 sq ft: about 1.2 gallons of penetrating oil stain on weathered wood, or under a gallon on smooth boards. Add railings before you buy: 24 feet of railing adds about 84 sq ft and usually pushes the order to 2 gallons.
How much does a gallon of deck stain cover?
Labels often say 200-300 sq ft, but that assumes smooth new wood. On weathered decking, a penetrating oil stain typically covers 100-150 sq ft per gallon on the first coat, and water-based semi-transparent stain around 150 sq ft. Solid stains and deck paint go further, around 200-300 sq ft.
Does a deck need one coat of stain or two?
Penetrating oil stains: usually one proper application (sometimes two passes wet-on-wet) - the wood takes what it can absorb, and a heavy second coat just sits on top and gets sticky. Water-based and solid stains: typically two thin coats for even color and film build. Check the can; the calculator handles either.
Should I use a sprayer, roller or brush?
Any of them, as long as you back-brush. A pump sprayer or pad applicator is fastest on the floor; a brush is best on railings and for working the stain into the grain. The brush is the one tool you shouldn't skip.
How often should you stain a deck?
Every 1-3 years for the floor with a penetrating or semi-transparent stain, and every 3-5 years for vertical surfaces like railings and fences, which get less sun and no foot traffic. When water stops beading and soaks straight in, it's time.
Why does weathered wood need so much more stain?
Years of sun and rain open the grain and dry the fibers, so the first coat disappears into the boards instead of spreading. Coverage on grey, thirsty decking routinely runs 40% below the label rate.
Should I include the underside or the fascia boards?
Fascia and stair stringers, yes: add their rough square footage to the floor area (a 16-ft fascia board about 1 ft wide is 16 sq ft). Undersides are usually left bare unless they're visible from living space below.
Related reading
Not sure which kind of finish to use? Paint or stain a deck weighs the two, and oil vs water-based deck stain helps you choose the stain. For more tools and calculators, see the wood paint and finish hub.