Deck Board Quantity Calculator

Work out deck board quantity instantly with clear inputs, formula shown and shareable results.

About Deck Board Quantity Calculator

Decking rows are set by the board pitch, the board width plus the drainage gap. Rows equal deck width divided by that pitch, and total linear metres is rows times deck length. Converting to a purchase quantity divides by the stock length and adds a small allowance for end cuts.

Formulas

Rows

Rows = ceil(deck width / (board width + gap))

Boards

Boards = ceil(rows x deck length / stock length x 1.05)

Worked example

With the default values below, Deck Board Quantity Calculator returns Boards required at 3.6 m of 41. Change any input above and every figure here is recalculated in your browser.

Inputs used

Deck lengthminimum 0.1 m: 5 m
Deck widthminimum 0.1 m: 4 m
Board widthminimum 20 mm: 140 mm
Gap between boardsminimum 0 mm: 5 mm

Results

Boards required at 3.6 m: 41
Rows of decking: 28
Total linear metres: 140.0 m
Deck area: 20.00 m²

Step by step

1Values used
2Rows
3Boards
4Boards required at 3.6 m= 41
5Rows of decking= 28
6Total linear metres= 140.0 m
7Deck area= 20.00 m²

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is the Deck Board Quantity figure worked out?

Rows = ceil(deck width / (board width + gap)). Decking rows are set by the board pitch, the board width plus the drainage gap.

Why leave a gap between boards?

It lets water drain and debris fall through, and it accommodates the seasonal movement of timber. Too tight a gap causes cupping and standing water.

What values do I need to enter?

This calculator takes 4 inputs: Deck length, Deck width, Board width, Gap between boards. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.