How much decking or flooring do I need?

The method

Each board covers its length multiplied by its width plus the gap. Add an allowance for cuts and selection, then divide.

boards = area × (1 + allowance) ÷ (length × (width + gap))

A 10% allowance is a common starting point, not a Kitaru specification. The right figure depends on your layout and on the natural variation of reclaimed timber; diagonal layouts and many cut-outs need more.

Example 1: a 40 m² deck

Boards of 18 × 100 × 3600 mm with a 5 mm gap: each board covers 3.6 m × 0.105 m = 0.378 m². With a 10% allowance you need 44 m², that is 44 ÷ 0.378 = 116.4, so 117 boards.

Example 2: a 25 m² floor

Tongue-and-groove boards of 15 × 150 × 1700 mm, no gap: each board covers 1.7 m × 0.15 m = 0.255 m². With a 10% allowance you need 27.5 m², that is 27.5 ÷ 0.255 = 107.8, so 108 boards. The covered width of a tongue-and-groove board can be slightly less than its nominal width, so we confirm quantities on your drawings.

Fasteners

A board crosses as many joists as its length divided by the joist spacing, rounded down, plus one. With 3600 mm boards on joists every 40 cm, that is 9 + 1 = 10 joists. At two screws per joist, that is 20 screws per board; with hidden clips, about one clip per board at each joist, 10 per board.

For the 40 m² deck above, the estimator gives 106 boards before allowance, about 2,226 screws if face-fixed (with a 5% spare), or about 1,113 hidden clips. Screws and clips are alternatives, so choose one method.

Common mistakes

• Ordering exactly the area, with no allowance for cuts and for reclaimed colour or marks you may set aside.
• Ignoring the joist layout: boards should end on a joist, so lengths and joist spacing should be planned together.
• Ordering in several batches: reclaimed timber varies from lot to lot, so order what you need in one go where possible.
• Forgetting hardware: screws, clips and post bases are quoted separately.