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Timber & Carpentry · quantity estimator

Decking Board Calculator

Estimate the board rows and linear metres for a rectangular deck using your chosen board direction, actual board width, planned gap and supplier stock length.

0% extra by defaultBoard direction mattersStock length required
Construction illustration for decking board quantity planning

Calculate decking rows and stock-board equivalents

Measure the deck as built or from a current drawing. Choose the direction the boards will run, then use the actual board face width and planned installed gap for your chosen system.

Which way will the boards run?
The run dimension becomes the length of each board row; the other dimension is the width to cover with rows.
m
Actual finished deck dimension.
m
Actual finished deck dimension.
mm
Use the installed face width of the exact board you intend to buy—not a generic decking width.
mm
Use the gap required for your product, fixing system and installation conditions. No gap is assumed.
m
Enter the length sold for the exact board you are pricing.
%
Optional. Starts at 0%. Add only an allowance you have deliberately chosen for cuts, selection or spares.
What the calculator does: rows are based on the deck width to cover and your board-plus-gap pitch. The stock-board figure is then a linear-metre equivalent, not an optimised butt-joint schedule.
Enter the real deck and board measurements.The result will separate board rows, net linear metres and whole stock-board equivalents.

Use the board direction before you count boards

A rectangular deck has two dimensions, but the board direction decides which one is the run length and which one must be covered by repeated board rows. Rotating the boards can therefore change the number of rows, the total linear metres and how efficiently merchant lengths can be cut.

1. Set the run

Choose whether boards run along the deck length or width.

2. Set the row pitch

Use the actual board face width plus the planned gap between rows.

3. Convert to stock

Round rows first, then convert net linear metres into the stock length actually sold.

The calculation

Rows = smallest whole number that covers the deck width

For a simple field of full-width boards: rows = ceil((width to cover + gap) ÷ (board face width + gap)). Net linear metres = rows × board run length. Optional extra is applied to the linear target before converting to whole stock lengths.

This row formula recognises that there is a gap between rows, not after the final board. Edge trims, picture frames, breaker boards, fascia and special perimeter details are separate measured items and are not invented by this tool.

Worked example

Suppose boards run along a 5.00 m deck length and must cover 4.00 m across. With a 120 mm board and a deliberately chosen 5 mm gap, the row pitch is 125 mm.

The field requires 33 rows, giving 165.00 linear metres of decking before any optional extra. If the chosen board is sold in 4.8 m lengths, simple linear conversion gives a minimum equivalent of 35 whole stock boards at 0% extra—but because each 5 m run is longer than one 4.8 m board, the real cutting/butt-joint layout must be planned separately.

Why there is no default board width, gap or stock length

Current UK merchant ranges demonstrate the variation. Wickes lists timber deck boards in different widths and lengths, including 120 mm and 144 mm boards and lengths from 1.8 m to 4.8 m. Travis Perkins likewise lists different finished widths and 3.0 m, 3.6 m, 4.2 m and 4.8 m examples. Composite systems add their own installation-gap requirements.

Current UK examples checked for this pass

Wickes timber decking boards · Travis Perkins timber decking · Trex UK board spacing example

Stock-board count is not a cutting plan

The whole-stock result answers a purchasing question using total linear metres. It does not prove that every individual row can be cut from that many boards. Long runs, staggered butt joints, breaker boards, picture frames, unusable offcuts and manufacturer joint rules can increase the real order.

  • Do not assume offcuts can be reused in the next row.
  • Do not hide picture-frame or fascia boards inside a generic waste percentage.
  • Do not use this surface-board result to size the supporting joists.

Planning estimate only. Confirm board dimensions, gaps, support/joint rules, structural framing and fixings against the exact product instructions and project design before ordering or building.

Continue the decking estimate

Decking Joist Calculator

Estimate the supporting joist layout separately from the surface boards.

Timber Length Calculator

Convert a known timber cutting-list total into merchant stock-length equivalents.

Decking Materials Estimator

Work through boards, joists and extra measured items as one project workflow.

Frequently asked questions

What is the effective installed cover width?

For repeated parallel rows, it is the board face width plus the planned gap to the next row. This calculator asks for both values so it does not assume either one.

Should I enter a gap for timber decking?

Enter the gap required by the exact decking system and its installation guidance. The calculator intentionally provides no universal gap.

Does the result include fascia, picture-frame boards or steps?

No. Measure those separately as real linear lengths so they are visible in the order rather than hidden inside a generic percentage.