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Deck stain calculator
Put your deck length, deck width, coats and coverage in: a 16 ft by 12 ft deck is 192 sq ft — 384 sq ft with 2 coats, 1.54 gal exact, 2 gallons to buy.
★ CONSTRUCTION · DECKS · STAIN
Deck Stain Calculator: 2 Gallons for a 16x12 ft Deck
On the defaults — a 16 ft by 12 ft deck, 2 coats, 250 sq ft per gallon — you need 2 gallons of deck stain. This is the deck stain tool: measure the deck once, allow for the coats, and buy the stain once — a half-stained deck waits for no second trip.
What does deck stain needed 2 gallons mean?
It means two gallons stain a 16 ft by 12 ft deck twice over. The deck itself is 192 square feet, since 16 times 12 is 192; with 2 coats that becomes 384 square feet of staining, and at 250 square feet per gallon the exact need is 1.54 gallons, rounded up to 2 whole gallons because stain is sold by the gallon, not by the fraction. The spare gallon is not spare stock exactly — it is the stain the job consumes in the second coat soaking into dry boards and in the brush and roller, so a deck stained to the exact gallon runs dry before the last boards.
Output · formula · meaning
| Output | Formula | What it means |
|---|---|---|
| Deck area | length × width | 192 sq ft — 16 × 12. |
| Area with coats | deck area × coats | 384 sq ft — 192 × 2. |
| Gallons | area with coats ÷ coverage, rounded up | 2 gallons — 384 ÷ 250, rounded up. |
Three things to check before you trust the number
First, check the coverage on the tin you are actually buying: 250 sq ft per gallon is the figure on the label, but a different product covers a different area, and the count follows the tin, not the deck. Second, remember the count follows the area times the coats, not the length alone: a 16 ft by 12 ft deck is 192 sq ft, and a deck measured by one side under-orders. Third, judge the coats honestly: stain soaks into dry boards, so 2 coats fits a deck in fair condition, but a weathered deck can drink a third coat, since every dry board takes stain twice. Boards, screws and railing are bought separately — see the decking calculator for the boards under the stain.
Worked example
16 ft long, 12 ft wide, 2 coats, 250 sq ft per gallon. Deck area: 16 × 12 = 192 sq ft. Area with coats: 192 × 2 = 384 sq ft. Gallons: 384 ÷ 250 = 1.536, or 1.54 gal exact, rounded up to 2 gallons to buy. In practice that means buying 2 gallons, and expecting the last gallon to go on the second coat soaking in and the brush and roller. If the same deck got only 1 coat instead, the need would fall to 1 gallon, but the deck stained would be half as well protected.
Every branch, checked
With a 20 ft long deck instead of 16 ft, the area rises to 240 sq ft and the exact need to 1.92 gal, but the buy stays 2 gallons, since 1.92 gal still fits two gallons. With a 16 ft wide deck, the area rises to 256 sq ft and the buy to 3 gallons, since 2.05 gal needs a third gallon. With 1 coat, the area with coats falls to 192 sq ft and the buy to 1 gallon. With 350 sq ft per gallon, the exact need falls to 1.1 gal but the buy stays 2 gallons. Deck size, coats and coverage each move the buy on their own, so a wrong coverage figure is as costly as a wrong measurement.
The reverses, worked backwards
The length behind 2 gallons is 16 ft: at 12 ft the need is 2 gallons (144 sq ft deck, 288 sq ft with 2 coats, 1.15 gal exact, 250 sq ft per gallon); at 20 ft it is 2 gallons (240 sq ft deck, 480 sq ft with 2 coats, 1.92 gal exact, 250 sq ft per gallon). The coats behind 2 gallons are 2: at 1 coat the need is 1 gallon (192 sq ft deck, 192 sq ft with 1 coat, 0.77 gal exact, 250 sq ft per gallon); at 3 coats it is 3 gallons (192 sq ft deck, 576 sq ft with 3 coats, 2.3 gal exact, 250 sq ft per gallon). The coverage behind 2 gallons is 250 sq ft per gallon: at 200 the need is 2 gallons (192 sq ft deck, 384 sq ft with 2 coats, 1.92 gal exact, 200 sq ft per gallon); at 300 it is 2 gallons (192 sq ft deck, 384 sq ft with 2 coats, 1.28 gal exact, 300 sq ft per gallon). Each reverse moves one input and holds the rest, so the step is exactly one dimension, coat or coverage change.
What the defaults assume
The defaults assume a 16 ft by 12 ft rectangular deck, 2 coats of stain, and 250 sq ft per gallon from the tin. They do not assume boards, screws, railing or stairs — a deck with stairs needs its stair boards stained separately, and the railing is stained by the foot, not by the gallon.
Who uses this
- A homeowner staining a deck: the 2-gallon buy settles the paint-store call before the first brush is loaded.
- A DIY builder restaining a backyard deck: the same maths on the deck alone gives the gallons, not a whole house.
- A contractor quoting a job: deck area, coats, coverage — the quote follows the same three steps, and the coat line shows the client why.
- A landlord budgeting a deck refit: the deck size off the plans, multiplied out, gives the gallon line on the refit budget.
Accuracy & limitations
The arithmetic is exact for the inputs entered; the judgement is the coats and the coverage. Real decks have stairs, angles and weathered boards, and the tin on the shelf overrides any planning figure; a deck measured gross over-orders, and a coverage figure read off a different product under-orders. Treat 2 gallons as the planning buy for a 16 ft by 12 ft deck at 2 coats and 250 sq ft per gallon, and add a third coat for a weathered deck that drinks stain.
Cite this calculator
Bright Side Kit, “Deck Stain Calculator: 2 Gallons for a 16x12 ft Deck”, https://brightoolbox.com/deck-stain-calculator/, accessed 3 November 2026. Students and researchers: cite the calculator name, the page URL and the date you used it, and quote the defaults (16 ft × 12 ft deck, 2 coats, 250 sq ft per gallon) so the 2-gallon result can be checked.
Frequently asked questions
How many gallons of stain do I need for a 16x12 ft deck?
2 gallons at 2 coats and 250 sq ft per gallon. The area is 192 sq ft; with 2 coats that is 384 sq ft, and 384 ÷ 250 = 1.536, or 1.54 gal exact, rounded up to 2.
How do I work out deck stain from a deck size?
Multiply length by width for the area, multiply by the coats, divide by the coverage and round up. A 16 ft by 12 ft deck is 16 × 12 = 192 sq ft, or 2 gallons at 2 coats and 250 sq ft per gallon.
How many coats of deck stain should I apply?
2 coats for a deck in fair condition, 3 for a weathered deck that drinks stain. Every coat is another full deck area of stain, so the coats move the buy directly.
Does this count the railing too?
No — this calculator counts deck boards only. Railing and stairs are stained by the foot and counted separately.
Should I buy the exact gallons or round up?
Round up: stain is sold by the gallon, and the spare gallon is the soaking and brush stock. A deck stained to the exact gallon runs dry before the last boards.
What if my deck is not a rectangle?
Split it into rectangles, work out each area, and add them before multiplying by the coats. The square footage calculator handles the area step section by section.