Decking Calculator: measuring notes and method
Measure across and along the boards
Width is across the rows; length is the distance along each row. Reversing board direction changes both the row count and the required board length.
Check stock lengths and details
Compare row lengths with available stock before ordering. Keep stairs, picture-frame borders and field boards identifiable in the cut schedule.
CHECK A PRACTICAL EXAMPLE
Changing board direction changes the order
A 6 × 4 m deck uses illustrative 140 mm boards with 5 mm gaps and no waste. Each row must be one full-length board in this model.
Boards run along 6 m
- Boards to buy
- 28
- Rows before waste
- 28
Boards run along 4 m
- Boards to buy
- 42
- Rows before waste
- 42
The required board length changes as well as the row count. Check available lengths and the specified support layout; the arithmetic comparison does not decide the permitted board direction.
Fixed comparison in metric units. Values are illustrative unless linked to a recorded project; changing the calculator above does not change this example.
Formula
Board rows = (deck width + gap) ÷ (board width + gap), rounded up. Apply waste and round up again.
Worked examples in metric and imperial units
Illustrative values match Reset example and stay fixed when you edit the calculator. Both columns describe the same calculation; converted inputs are rounded.
Metric worked example
- Length
- 6 m
- Width
- 4 m
- Board face width
- 140 mm
- Board gap
- 5 mm
- Waste allowance
- 10 %
Boards to buy: 31
Imperial worked example
- Length
- 19.685 ft
- Width
- 13.1234 ft
- Board face width
- 5.5118 in
- Board gap
- 0.1969 in
- Waste allowance
- 10 %
Boards to buy: 31
Follow the calculation
Lengths in this working are in metres.
- Rows = (4 + 0.005) ÷ (0.14 + 0.005), rounded up.
- Multiply whole rows by 1.1 and round up for spare boards. Each board is assumed to span 6 m.
Reviewed 19 October 2026. How calculations are checked · Report a correction