Siding clapboard calculator

Count clapboard courses from exposed height, then whole boards per course.

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Wall height

Wall width

More inputs and assumptions

Exposed height per course

Board length

Extra allowance (%)

Answer

…

Count clapboard courses from exposed height, then whole boards per course.

More results

Precision and calculation record

Decimal places in numeric results and text downloads

Rounding changes displayed numbers, not the calculation. Text, fractions, matrices and CSV schedules keep their own formatting. Automatic keeps up to 12 significant digits, with money shown to cents where applicable.

Saved scenario

Save the current answer, then change an input to compare. This clears when you leave.

Formula and assumptions

Courses = ceiling(wall height/exposure). Each course uses ceiling(wall width/board length) boards. This conservative layout does not reuse offcuts across courses or subtract openings. Use exposure after overlap, not full board width.

Automatic precision shows numbers to 12 significant digits. Thousands separators such as 1,000 are accepted; use a dot for decimals.

Scratch calculator

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Updated 2026-09-26

Using Siding clapboard calculator

Count clapboard courses from exposed height, then whole boards per course.

Next: Board foot calculator

A worked example

Example inputs: wall height = 3, wall width = 10, exposed height per course = 0.15, board length = 4, extra allowance (%) = 10. Courses required = 20.

Before you use the result

Example results for wall height

These examples use Wall width: 10; Exposed height per course: 0.15; Board length: 4; Extra allowance (%): 10. They are reference calculations, not recommended settings.

Wall height	Courses required
1.5	10
3	20
6	40

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ToolOctopus. “Siding clapboard calculator.” Updated 2026-09-26. https://tooloctopus.com/siding-clapboard-calculator.

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