Deck board calculator
Board count comes from the deck width divided by the board module, which includes the drainage gap.
%
Deck boards to buy
42
- Rows of boards
- 27
- Linear metres of decking
- 148.5
- Joists
- 14
- Joist timber
- 56.0
- Screws
- 756
- Deck area
- 20.00
- Linear metres per square metre
- 7.43
Show the working
- Deck length = 5
- Deck width = 4
- Board width = 145
- Gap between boards = 5
- Board length = 3.6
- Joist spacing = 400
- Waste allowance = 10
- Deck area = 5 * 4 = 20
- module = (145 + 5) / 1000 = 0.15
- Rows of boards = ceil(4 / 0.15) = 27
- Linear metres of decking = 27 * 5 * (1 + 10/100) = 148.5
- Deck boards to buy = ceil(148.5 / 3.6) = 42
- Joists = ceil(5 / (400/1000)) + 1 = 14
- Joist timber = 14 * 4 = 56
- Screws = ceil(27 * 14 * 2) = 756
- Linear metres per square metre = 20 > 0 ? 148.5 / 20 : 0 = 7.425
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- rows = ceil(deck width / (board width + gap))
- linear metres = rows x deck length x (1 + waste)
Leave a gap even with grooved boards. Timber swells when wet and a tight deck will buckle.