Deckboard / the calculation guide
From a rectangle
to a board takeoff.
A board order is useful when you can trace the number back to the layout. Deckboard uses a deliberately conservative row-by-row model: a single rectangle, parallel rows and a separate stock board for every segment.
Measure the direction first
The board run follows the board length. The cross width crosses the rows at a right angle. Swapping them can change the whole-board count, especially when the run becomes longer than your stock. Enter millimetres throughout: 4.8 metres is 4,800 mm.
Use actual board face width, rather than a nominal product name. The face width excludes the gap. Your stock length should be the usable length after any end trimming you want to reserve; the calculator does not subtract a hidden trim allowance.
Count rows, then check the final strip
For n rows, the combined width is n × face width + (n − 1) × side gap. Deckboard takes the smallest whole row count whose combined width reaches the cross width. It then calculates the actual face left for the last row.
Rows = round up [(cross width + side gap) ÷ (face width + side gap)]
Last-row face = cross width − (rows − 1) × (face width + side gap)
The layout starts with a full-width board on one side and ends with a ripped board on the other. It does not centre the layout, share the rip between two edges, add perimeter gaps or make a border frame.
There is one useful edge case: a requested outside dimension can fall inside the final side gap. That would produce a zero or negative last-board face, so the calculator stops and asks you to change the dimension or gap. It does not silently treat empty space as a board.
Example 1: full-length rows
Take a 4,800 mm board run and a 3,000 mm cross width, using 140 mm boards and 5 mm side gaps. The row calculation is 3,005 ÷ 145 = 20.724… so it needs 21 rows. Twenty full row pitches use 2,900 mm, leaving a 100 mm last-row face.
With 4,800 mm usable stock, each row uses one board: 21 base stock boards. Adding 10% means 21 × 1.10 = 23.1, rounded up to 24 stock boards. The extra three are stock boards, not an automatic statement about damaged timber.
Longer runs and equal-length segments
With joints disabled, a run longer than stock is rejected. Enabling segments is an explicit alternative. The model chooses the smallest number of equal-length pieces that fit the usable stock after the gaps between their ends are removed from the total run.
Segments per row = round up [(board run + joint gap) ÷ (stock length + joint gap)]
Each segment = [board run − (segments − 1) × joint gap] ÷ segments
Every segment receives its own stock board. This simple counting rule deliberately makes no attempt to nest several short pieces into a stock board or reuse offcuts in another row. It can therefore order more timber than an optimised cutting plan. The displayed unused stock is a length difference before saw cuts or further trimming; it is not promised reusable material.
Example 2: two segments in each row
Keep the same 3,000 mm width and 21 rows, but use a 6,000 mm run, 3,600 mm stock and a 3 mm end joint gap. Two segments are needed. Each segment is (6,000 − 3) ÷ 2 = 2,998.5 mm. Each row uses two stock boards, making 42 base boards. A 5% extra allowance produces 44.1, rounded up to 45 stock boards.
All row joints line up in this abstract equal-segment drawing. It is not an instruction to build that joint pattern. Joint position, required support, fixings, permitted gaps, product movement and structural suitability must be determined for your actual materials and layout.
What the result includes
- Whole rows and stock boards, with one last-row width check.
- Equal segment length, joint count per row and a transparent extra-stock allowance.
- Nominal finished board length and the stock length ordered.
It excludes joists, supports, stairs, diagonal layouts, irregular boundaries, picture-frame borders, hardware and product selection. A narrow positive last row is shown numerically; the calculator does not decide whether that strip is suitable to install.
Keep the checked version
Copy or print the result after calculation. It includes the inputs and conservative assumptions. Input measurements remain in this tab and are not automatically saved. Displayed segment lengths may be rounded to three decimal places; all row and board rounding uses the unrounded integer-ratio arithmetic.