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Ceiling Joist Count Calculator

Joists for a rectangular ceiling at given OC spacing.

Compute the number of ceiling joists required to span a rectangular ceiling, given the span direction (joists run perpendicular to the longer dimension) and the on-centre spacing.

Marcus Laurent By Marcus Laurent
Published Last reviewed 1 min read

Inputs

ft
ft

Results

Enter values and click Calculate to see results.
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How to use this calculator

  1. Fill in the inputs above using the units you already have.
  2. Values update automatically as you type — no submit button needed.
  3. Hover any result row for the underlying formula and intermediate values.

Formula

Joists = ceil(perpendicular_span_ft · 12 / spacing_in) + 1.

In depth

Compute the number of ceiling joists required to span a rectangular ceiling, given the span direction (joists run perpendicular to the longer dimension) and the on-centre spacing.