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Garden & planters

Decking board calculator

Estimate the surface boards for a rectangular deck by counting each row. The model keeps length offcuts separate: it gives a conservative order quantity without assuming that every offcut can be used elsewhere.

Your project measurements

Metric units
m
m
m
mm
mm
Refer to the material’s instructions. This calculation does not prescribe a gap.
%
Your project assumption. It is added to the required quantity before rounding up to whole packs.

Need a starting point? The initial values are an example.

YOUR ESTIMATE

23 boards

Whole boards required

Illustrative diagram. Board arrangement in rows, without structural design. Result: 23 boards4 m3 mRows: 21 · boards per row: 1Illustrative diagram23 boards
Rows across the width21 rows
Whole boards per row1 board
Boards before reserve21 boards
Row length84 m
Purchased length92 m
Extra length purchased8 m

Conservative count per row: offcuts are not reassigned to later rows. The last row may need to be cut to width.

Enter the usable dimensions after any edge gaps specified in your project. Joints at board ends do not reduce the calculated requirement here.

This result covers only the surface boards: it does not size supports, spans or fixings, or calculate loads.

Understand the calculation
  1. Width: (3 + 0.005) ÷ (0.145 + 0.005) = 21 rows after rounding.
  2. 4 m per row ÷ 4 m per board = 1 whole board per row.
  3. 21 × 1 = 21 boards, without reusing offcuts.
  4. With a 5% reserve and rounding: 23 boards, or 92 m purchased.

The estimate depends on your measurements and entered inputs. PDF output uses your browser’s Save as PDF option.

MetraNest · https://metranest.com/en/calculators/decking-boards/ · Méthode : Rangées = arrondi supérieur de (largeur de zone + écart) ÷ (largeur de lame + écart). Lames par rangée = arrondi supérieur de longueur de zone ÷ longueur de lame. La réserve s’applique au nombre total.

Choose the row direction

The boards follow the length of the entered area. The width determines the number of rows, using the side gap you enter. To compare the other direction, swap length and width. Use your project’s usable dimensions after accounting for any perimeter gaps specified in its design.

Count whole boards per row

Each row is allocated enough whole boards to reach the required length. The result multiplies this number by the number of rows, then adds the reserve. Offcuts are not reassigned. This method may buy more than an optimised cutting plan, but it avoids concealing waste behind a simple total of linear metres.

Separate quantities from design

The last row may need to be cut to width. End joints do not reduce the calculated requirement. The diagram and result cover only the visible decking: they do not define joists, supports, spans, fixings or permissible loads. These elements depend on the chosen system and its design.

The formula
Rows = (area width + gap) ÷ (board width + gap), rounded up. Boards per row = area length ÷ board length, rounded up. The reserve is applied to the total count.

Short boards for a length of 4.5 m

For 4.5 × 2 m, with boards measuring 2.4 m by 120 mm and an entered gap of 5 mm, the model counts seventeen rows. Each needs two boards: thirty-four boards, or 81.6 m purchased before any extra reserve.

Details to check

  • Check the millimetre and metre units.
  • Compare both orientations.
  • Check the cuts on a sketch before ordering.

Frequently asked questions

Can offcuts reduce the order?

A precise cutting plan may sometimes reuse them. This conservative calculation does not assume that.

Does the tool calculate deck supports?

No. The result is limited to surface boards and does not validate any structure.

Method and references · Editorial review: 25 October 2026

The geometric formulas are explained here. For a product, its packaging dimensions and coverage rate remain the reference inputs.

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