Solve backwards
How big a deck will my deck boards cover?
- 50 boardsThe example worked below
- Deck Board CalculatorEvery figure is its own
You have
How much deck boards?
Worked by the Deck Board Calculator at the settings below.
The settings it uses
- Board Length
- 12 ft
What it will do
206 sq ft of deck
19.1 m²
One deck. Enough for a deck 17.6 × 11.7 ft.
Or several. Less than one deck of the size the Deck Board Calculator opens on (a deck 19.5 × 13 ft).
Check it forwards
- Deck Length
- 17.6 ft
- Deck Width
- 11.7 ft
- It asks for
- 50 boards
- You have
- 50 boards
The Deck Board Calculator asks for 50 boards at that size, and 52 boards one step larger.
If you had more, or less
Around your amount
Each worked by the Deck Board Calculator at the same settings.
Half
25 boards
96 sq ft
a deck 12 × 8 ft
Yours
50 boards
206 sq ft
a deck 17.6 × 11.7 ft
Half as much again
75 boards
384 sq ft
a deck 24 × 16 ft
Double
100 boards
384 sq ft
a deck 24 × 16 ft
Common amounts
What each amount of deck boards covers
The sizes it is usually sold in, each worked by the Deck Board Calculator at the settings above.
| You have | It covers | As one deck | Average decks |
|---|---|---|---|
| 20 boards | 96 sq ft(8.92 m²) | a deck 12 × 8 ft | under 1 |
| 50 boards | 206 sq ft(19.1 m²) | a deck 17.6 × 11.7 ft | under 1 |
| 100 boards | 384 sq ft(35.7 m²) | a deck 24 × 16 ft | 1 |
| 150 boards | 824 sq ft(76.5 m²) | a deck 35 × 23 ft | 2 |
A board and a gap every five and five-eighths inches
A standard 5/4 by 6 deck board is about 5½ inches wide, and with a ⅛ inch gap for drainage and seasonal movement each row takes 5⅝ inches, about 143 mm. Narrower composite or hardwood boards need more rows for the same deck — at 5¼ inches about five per cent more — so check the board you bought.
Every row is whole boards
The calculator works out the boards per row once and multiplies by the rows, so a row that needs just over one board takes two, and the offcut is never carried to the next row. That is why the deck grows in steps as the boards do, and why reusing tails — where seams can land on a joist — stretches a stack further.
No boards spare for rejects
Nothing is added for boards culled for crown, cup or splits, for ripping the outermost row to width, or for cuts around posts and openings. Ordering exactly the count leaves nothing to reject, so the deck a stack makes in practice is a little smaller than the one shown — keep a few boards back.
How the answer is worked
Nothing here is a second formula. The Deck Board Calculator runs forwards — a size in, a quantity out — and this page grows its own starting deck in proportion until the quantity it asks for is what you have. Where it rounds up to whole containers, the answer is the largest size before the next one would be needed.
Where the calculator adds an allowance for cuts or breakage when you order, the same allowance comes off here, because it is the same calculator: a stack you already own finishes less than its face value. Where it adds none, neither does this page — the settings beside the answer say which.
Deck Board Calculator
runs it forwardsEstimate how many deck boards you need, accounting for board width and the gap left between boards.
Work out what to buy insteadSolve backwards
Other things you might already have
How much floor will my tiles cover?
Floor tile, worked by the Floor & Wall Tile Calculator.
How big a patio will my pavers make?
Pavers, worked by the Paver Calculator.
How much wall will my bricks build?
Bricks, worked by the Brick Calculator.
How much wall will my concrete blocks build?
Concrete blocks, worked by the Concrete CMU Block Counter & Grout Infill Calculator.
How long a retaining wall will my blocks build?
Retaining wall blocks, worked by the Retaining Wall Block Calculator.
How much fence will my pickets cover?
Fence pickets, worked by the Fence Picket Calculator.
Solve backwards
Start from what is already in the yard
Paint, sheets, rolls, bags and pieces, each read the other way by the calculator that orders it.
The calculator's own figures
Nothing is estimated twice: the page runs the same calculator you would order with.
The largest size that fits
Where a calculator rounds up to whole containers, the answer stops before the next one.
Both unit systems
Gallons and litres, square feet and square metres, side by side.
Frequently asked questions
- How much deck does 50 boards of deck boards cover?
- At the Deck Board Calculator's own settings, 206 sq ft (19.1 m²) — a deck 17.6 × 11.7 ft. Every figure follows the settings, which you can change in the calculator.
- How many deck boards do I need for a 12 by 12 deck?
- With 5½ inch boards and ⅛ inch gaps, 12 feet of width takes about 26 rows, and 12 foot boards cover each row in one — so about 26 boards of 12 feet, plus a few for rejects and ripping the last row. In metric, a 3.6 by 3.6 metre deck needs about the same.
- What gap should I leave between deck boards?
- Commonly ⅛ to ¼ inch (3 to 6 mm) between boards, for drainage and seasonal movement — wet pressure-treated boards are sometimes laid tight because they shrink as they dry. Composite and hidden-fastener systems set their own gap. The gap changes the row count slightly.
- Is it better to buy longer deck boards?
- Longer boards mean fewer seams and usually less waste when they span the deck in one, but cost more per board and are harder to handle. The best length is the one that divides the deck into whole boards with seams landing on joists — the calculator shows how the rows divide.