basic

Window-AC BTU Sizing from Room Area Calculator

BTU/hr ≈ 20 · sqft · ceiling_factor · sun_factor · occupant_extra.

Estimate the cooling capacity (BTU/hr) needed for a window-AC unit based on the EnergyStar rule of thumb of ~20 BTU/hr per square foot, scaled for ceiling height (× ceiling/8), sun exposure (1.0 default, 1.10 sunny, 0.90 shaded), and additional 600 BTU/hr per occupant beyond the first two. Reports BTU/hr and the recommended unit size band.

Marcus Laurent By Marcus Laurent
Published Last reviewed 1 min read

Inputs

ft²
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

BTU = 20·sqft·(ceiling/8)·sun + 600·max(0, occupants − 2).

In depth

Estimate the cooling capacity (BTU/hr) needed for a window-AC unit based on the EnergyStar rule of thumb of ~20 BTU/hr per square foot, scaled for ceiling height (× ceiling/8), sun exposure (1.0 default, 1.10 sunny, 0.90 shaded), and additional 600 BTU/hr per occupant beyond the first two. Reports BTU/hr and the recommended unit size band.