How to use it
- Choose the Units and measure the deck's Deck length and Deck width, with the boards running along the length.
- Enter the Board width and the Board length of the boards you buy, and the Gap between boards you plan.
- Set the Waste allowance for cut ends and damaged boards.
- Read Boards to order, Rows of boards and Boards per row.
How the boards are counted
The boards run along the length of the deck. Each row is one line of boards laid side by side across the width, with a gap between each pair, so the rows are counted across the width.
A row is made of boards of the board length. When a row is longer than one board, the boards are joined end to end and the last one is cut, so the count rounds up. The waste is then added to the whole count.
rows = (deck width + gap) ÷ (board width + gap), rounded up
boards per row = deck length ÷ board length, rounded up
boards to order = rows × boards per row × (1 + waste), rounded upWhat the count does not include
- Boards laid at an angle, such as a diagonal or herringbone pattern. They need more boards and a different count.
- Boards laid the other way across the deck. Enter the deck's width as the length, and the length as the width.
- Joists, fixings, border boards and the fascia. Each of these needs its own length.
Worked example: a 4.8 m × 3.6 m deck with 140 mm boards 3.6 m long, 5 mm gaps and 10 % waste
The rows are (3,600 + 5) ÷ (140 + 5) = 24.86, rounded up to 25. Each row needs 4,800 ÷ 3,600 = 1.33 boards, rounded up to 2.
25 × 2 = 50 boards, and with 10 % waste 55 boards to order. The deck area is 4.8 × 3.6 = 17.28 m².
| Result | |
|---|---|
| Rows of boards | 25 |
| Boards per row | 2 |
| Boards to order (10 % waste) | 55 |
| Deck area | 17.28 m² |
Frequently asked questions
Why are the boards counted in rows and not by area?
The board width and the gap decide how many boards fit across the width, and the area alone leaves both out. Each row covers one board width plus one gap, while the length sets how many boards each row needs.
How much waste should I allow?
The waste allowance is your own choice. It covers cut ends, split boards and pieces you reject. A diagonal lay, or a deck with many corners and steps, usually needs a larger allowance than a plain rectangle.
What if my boards are shorter than the deck?
Join them end to end in each row and stagger the joins so they do not line up. The count rounds up the boards per row, so the cut pieces at the joins are covered by the waste allowance.
Can I use this for a deck that is not a rectangle?
The count is for a rectangle. For an L-shaped or irregular deck, split the area into rectangles, count each one, and add the boards together, with the joins between the parts covered by the waste allowance.
Does the tool store what I enter?
No. The count runs in your browser, and nothing you type is sent to us or stored.
Sources
Figures and text last checked on Thursday, November 12, 2026.