Estimate boards for a deck before you buy
Deck area ÷ board coverage undersells the gaps and the cuts. Count rows, then boards per row, then waste.
Tools used in this guide
The job
Decking maths goes wrong in two places: the 3–8mm gap between boards changes the effective width, and boards don't come in your deck's exact length — offcuts and staggered joints mean buying waste on purpose.
Measure, enter, count
Deck length and width in metres, board face width and gap in millimetres, the sold board length, and a waste percentage (10% is the usual allowance). Out come rows needed, boards per row, and total boards with waste.
- A 6m × 4m deck with 140mm boards at 5mm gaps is 28 rows — at 4m board length, 2 boards per row plus staggering.
- Diagonal or herringbone layouts need more waste — bump it to 15%.
What it doesn't include
This is decking boards only — joists, screws, fascia and the frame are separate lists. Check local code for gap rules (some climates want wider gaps for drainage).