Lumber Calculator
Calculate how many boards and board lengths you need for a deck, fence, or siding project.
How to use the calculator
- Measure the deck's length in the direction of the boards, and the width across.
- Enter the board width and desired gap between boards (common for drainage on decks).
- Enter the board length you're buying in (standard lumber is often sold in fixed lengths like 3, 4.2, or 4.8 m).
How is it calculated?
The number of board rows is calculated from the deck's width divided by board width plus gap. Total board length is the number of rows multiplied by the deck's length. The number of board pieces you need to buy is total board length divided by the length per piece, rounded up.
Frequently asked questions
Why does "board rows" matter?
It's the number of boards needed across the width to cover the whole area — each board in a row runs along the entire deck length (or is joined if the length exceeds the available board length).
Should I buy a bit extra?
Yes, it's recommended to buy 5–10% extra to cover cutting waste, joints, and any miscuts — the calculator only shows the theoretical minimum.
Does this only apply to decking boards?
No, the same principle works for fence boards, siding, and other projects where you lay boards in rows with a given gap.