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Decking Calculator

Estimate deck boards from surface area, actual board width, gap, stock length and cuts.

Units
Your measurements
in
ft
Adjust estimate

Waste, compaction, density and price. Sensible defaults are already applied, and whatever is in use is listed under the result.

in
%

Result

You need 43 boards to cover the area.

Based on: 0% allowance

Count before roundingest.
42.7boards
Area including allowanceest.
240ft²

How the decking calculator works

The count is adjusted deck area divided by the face coverage of one board. The tool uses actual width and the entered gap.

Board direction, breaker boards, picture framing and available lengths determine real cut efficiency. This is quantity planning, not a framing design.

Formula used for decking calculator

The calculator keeps the measured quantity separate from any purchase rounding or allowance.

  1. Board coverage(actual width + gap) ÷ 12 × stock length
  2. Adjusted deck areasurface area × (1 + cuts allowance)
  3. Boardsadjusted area ÷ board coverage, rounded up

Planning choices for decking calculator

SituationUseWhy it matters
Straight full-length layoutMatch stock to spanMinimizes butt joints
Picture frame or diagonalDraw board layoutBorder and angle cuts change count
Multiple stock lengthsOptimize by runArea-only count cannot choose lengths

These are measurement and ordering choices, not structural specifications or code requirements.

Measure and order decking

Use actual board width. A nominal 6 in board commonly covers less than 6 in before any gap.

Confirm available stock lengths, end-trim requirements and whether spare full-length boards are wanted for future replacement.

Decking Calculator questions

  • Does the gap increase or decrease board count?

    A gap increases the pitch covered by each board, so it slightly reduces the count across a fixed width.

  • Does this size joists or beams?

    No. It calculates surface boards only and makes no structural recommendation.

  • Should I use deck area or footprint?

    Use the actual boarded surface area, including platforms that receive deck boards.

Variables and units

For the default “Surface area” mode. Other modes label their own fields in the calculator.

area
Area to cover: ft², yd², m².
boardWidth
Actual exposed width: in.
boardLength
Stock length: ft.
gap
Gap between boards: in; optional.
waste
Cuts and rejects allowance: %; optional.

Worked example: a 12 ft by 20 ft deck

Deck surface area is 240 ft², using 5.5 in by 12 ft boards, a 1/8 in gap and 10% cuts.

What goes in
FieldValue
Area to cover240 ft²
Actual exposed width5.5 in
Stock length12 ft
Gap between boards0.125 in
Cuts and rejects allowance10 %
What comes out
ResultValue
boards to buy47 boards
Area including allowance264 ft²

These figures are generated by the same calculation the calculator above uses, so they update automatically if the method changes.

Where these numbers come from

This calculator uses geometry and values shown in the form. Editable product dimensions, coverage figures, prices and allowances are inputs, not universal recommendations; confirm them against the product label, drawing or supplier quote.

Last updated:

Published by Material Totals. Review the calculation methodology and source registry.

Suggested citation: Material Totals, “Decking Calculator,” https://materialtotals.com/decking-calculator/