How many boards do I need for a 4 × 3 m deck?

With 120 mm boards, 5 mm gaps and 3.6 m board length: 24 rows × 2 boards per row = 48 boards (raw). Adding 10% waste brings it to ~53 boards.

Which board width is most common?

120 mm is the most common standard width in Northern Europe. 95 mm gives a finer look with more lines, while 145 mm suits larger decks with fewer joints.

How wide should the gap between boards be?

Typically 4–6 mm — most commonly 5 mm. The gap is critical for moisture, expansion and drainage. Too narrow and rainwater pools in the joints; too wide and the boards feel unstable.

How much waste should I budget for?

5–10% for a simple rectangular deck is standard. 15% for skewed corners, many posts, cutouts, or when board length doesn't match the deck dimensions cleanly.

How many deck boards do you need per m²?

Q: How many deck boards do you need per m²?

With a standard deck board 120 mm wide and a 5 mm gap (effective width 125 mm), you get about 8 boards per metre of deck width. Boards per m² depends on board length.

With a typical deck board of 120 mm width and 5 mm gap, the effective board width is 125 mm. That gives approximately 8 boards per metre of width.

Board widthEffective widthBoards per m width

95 mm100 mm10

120 mm125 mm8

145 mm150 mmapprox. 7

Effective width = board width + gap (typically 5 mm). Number of rows multiplied by boards per row gives the total board count.

Example: 4 × 3 metre deck

A deck measuring 4 metres in length and 3 metres in width with 120 mm boards and 5 mm gaps:

Area4 × 3 = 12 m²

Effective board width120 + 5 = 125 mm

Number of rows⌈3,000 ÷ 125⌉ = 24 rows

Boards per row (3.6 m board)⌈4 ÷ 3.6⌉ = 2 pcs

Total boards (raw)24 × 2 = 48 pcs

With 10% wasteapprox. 53 boards

Don't forget waste

Deck boards need to be cut at edges, corners and around posts. There's also a risk of defective boards in the delivery. 10% extra is a good starting point for most decks.

•5–10% — simple, rectangular deck
•15% — angled corners, many posts or cutouts

Common board lengths

Deck boards come in fixed lengths. Your choice of board length affects the number of boards per row — and therefore the total count.

2.4 mSmall decks and balconies

3.0 mPopular standard length

3.6 mMost used for medium-sized decks

4.2 mFor wider decks

4.8 mLongest standard size

Choose the board length that best matches your deck's length — this minimises waste and the number of joints.

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Use MyPlanDIY's free deck calculator — enter dimensions, board width and waste, and get the number of boards, screws and joists instantly.

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