Deck Stain Calculator

Understanding your result

The headline is the deck stain for the coats you chose, with the allowance, and the sub-line is the can list. The four figures show the area, the coverage used (the typical figure for the wood condition, or your can’s if you entered one), the stain per coat and the cans.

The breakdown shows the three parts of a deck as their own lines: the boards from length times width, the railings at 2 sq ft per foot, and the steps at 5 sq ft each. Then the wood condition with its typical coverage, and the usual per-coat, allowance, total and can lines. If the railings line is more than two-fifths of the total, the result says so, because the railings are where the time goes.

Deck stain is bought in gallons and 5-gallon pails and comes in one coat for most products, so the rounding is kinder than for paint. The fence stain calculator uses the same products for a fence, the wood stain calculator does furniture and interior woodwork, and the porch floor paint calculator is the right one if the deck is to be painted rather than stained.

How we calculate this

The board area is the deck’s footprint; the gaps between boards do not reduce it because the stain runs down the edges. The railing figure of 2 sq ft per linear foot is the two faces of a 36 in high railing with 2 × 2 balusters at 4 in spacing: the balusters, the top and bottom rails and the posts add up to about one square foot per foot per side. A solid privacy rail is nearer 1 sq ft per foot per side and a cable rail much less; adjust the railing length to suit. A step is a 3 ft wide tread of about 1 ft plus a riser of about 7 in, around 5 sq ft including the edges.

The coverage by wood condition is the main assumption. Exterior stain data sheets quote two figures, one for smooth new wood and one for rough or weathered wood, and the gap between them is the difference between a gallon and two. The deck stain guide explains the porosity behind it, with the water-drop test for new wood, and the coverage rates table lists the published ranges by product type. The rounding to cans is the same as everywhere on the site.

The assumptions behind the numbers

Assumptions last reviewed October 7, 2026.

The calculator does not model the cleaner or stripper, the brightener, or a second wet-on-wet application on very dry wood, which is better thought of as a heavier first coat; the rough condition allows for it. It does not model drying weather: the drying guide covers the two dry days most stains want before and after.

Two worked examples

Where to find your inputs

Length and width. The deck’s footprint, outside edge to outside edge. For an L-shaped deck add the two rectangles and enter the total as one with any width that gives the same area.

Railing length. Every run of railing, including the stair rail. Leave blank for a deck at ground level with no railing.

Steps. Count treads. Wide steps across the whole front of a deck count as one step per 3 ft of width.

Wood condition. New and smooth, sealed wood is the top figure; a deck that has been stained before and cleaned is weathered; grey, dried-out, never-finished wood is rough. When in doubt, choose the lower coverage and keep the leftover.

Common mistakes

• Forgetting the railings. Eighty square feet and half the day on a small deck.
• Staining wet wood. New treated lumber and a deck washed yesterday both shed stain. Water-drop test, two dry days.
• Two coats of a penetrating stain. The second cannot soak in and stays tacky. One coat, wet-on-wet.
• Trusting the smooth-wood coverage on an old deck. Weathered boards take nearly double.
• Staining in full sun. The stain flashes off before it penetrates and shows lap marks. Work in shade or early.
• Not back-brushing after a sprayer or pad. The stain pools on the surface instead of going in.

Questions people ask

How much stain does a 16 × 12 deck take?

The boards are 192 sq ft. With 40 ft of baluster railing (80 sq ft) and three steps (15 sq ft), the deck is 287 sq ft. On weathered wood at 175 sq ft per gallon, one coat with a 5% allowance is 1.72 gallons, so a gallon and three quarts. New, smooth wood at 300 sq ft per gallon would take about a gallon.

One coat or two?

Penetrating oil and semi-transparent stains are one coat, applied wet-on-wet until the wood stops absorbing; a second coat that cannot soak in stays sticky. Solid-colour stains and film-forming finishes take two. The product's data sheet is the final word, and the coats field accepts either.

How much stain do railings take?

About 2 sq ft per linear foot for a 36 in railing with balusters, both sides counted, which is the figure the calculator uses. Forty feet of railing is 80 sq ft, nearly half the boards of a small deck, and it takes longer than the boards because every baluster has four faces.

Can I stain new pressure-treated wood?

Not until it is dry. New treated lumber is wet from the treatment and sheds stain for weeks or months. Sprinkle water on a board. If it beads, the wood is not ready; if it soaks in, it is. Once dry, use the new-wood coverage.

Why does weathered wood take more stain?

The surface fibres have been raised and opened by sun and water, and old stain has worn to bare wood in places, so the first coat soaks into a much larger surface. Data sheets quote 150 to 250 sq ft per gallon on weathered wood against 250 to 400 on new, which is why the condition setting matters more than the brand.

Should I strip or clean first?

Clean always, with a deck cleaner and a stiff brush or a low-pressure wash, then let it dry for two days. Strip when the old finish is a solid stain or a film that is peeling, because new stain will not penetrate through it. A cleaned, brightened deck is the weathered condition in this calculator.