Deck board calculator
Calculate how many deck boards, screws, and total material you need. Adjust for board size, spacing, and waste.
Note: These results are a planning aid to help you get started. Local building codes vary, so please double-check requirements in your area before you buy materials or start construction.
How to calculate deck boards
- Enter your deck’s length and width.
- Pick a board width from the “Common board widths” dropdown, or type a custom width. A nominal “6-inch” board is actually 5.5 inches wide, and the calculator uses the actual width.
- Pick a board length from the “Common board lengths” dropdown, or type a custom length that matches what you have available.
- The result updates as you change inputs. For more control over spacing, waste, or layout, see Advanced options below.
Advanced options
Gap spacing controls the space between boards. The default is 5 mm (3/16 inch), which works for most pressure-treated lumber. Boards need a small gap for drainage and to allow for expansion and contraction with temperature changes. Wet boards may shrink as they dry, so a slightly wider gap is safer than going edge-to-edge.
Waste factor covers off-cuts and the occasional miscut. 10% is a reasonable number for most projects, roughly one extra board for every ten you install.
Joist spacing only affects the screw estimate, not the board count. The default is 400 mm (16 inches), which is standard for most residential decks. The calculator assumes two screws per board per joist, plus a small buffer for end joints.
Layout pattern defaults to Standard (Parallel), which is the most material-efficient option. If you switch to Diagonal, the calculator adds 15% to the total material needed, because angled cuts at both ends produce off-cuts that are harder to reuse.
Frequently asked questions
Why does switching to diagonal add more material?
A diagonal layout runs boards at 45 degrees across the frame. Each board needs to be cut at both ends, which leaves angled off-cuts that are less straightforward to reuse than square ends. Expect to need about 15% more material than a parallel layout.
My boards are wet from pressure treatment. Should I change anything?
Wet boards may shrink as they dry, so the gap you install with will tend to widen over time. A slightly wider gap is safer than going edge-to-edge. The default 5 mm gap is a sensible starting point for most treated lumber.
The screw count seems high. What’s included?
Two screws per board-joist intersection, plus the screws needed for any extra boards from your waste factor. That total tends to be larger than people expect, especially for tighter joist spacing.