Room BTU Calculator

Estimate a room's BTU size from dimensions, windows and occupants.

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Room BTU Calculator

How to use this tool

  1. Enter the room length and width in feet.
  2. Enter the number of windows and usual occupants.
  3. Press Generate to see the rough BTU estimate.

Worked example

A room 12 by 15 feet has an area of 180 square feet. At 20 BTU per square foot that is 3600, plus 2 windows at 1000 each gives 5600 BTU, and with 2 occupants there is no extra allowance, so the estimate is 5600 BTU.

What this tool does not do / Limits

This is a rough sizing estimate only. It ignores ceiling height, insulation, sun exposure, climate and heat from appliances, so measure and confirm with a qualified installer before buying equipment.

Frequently asked questions

Why do windows add BTU?

Windows lose and gain more heat than walls, so each window raises the heating or cooling load.

Is this enough to choose an air conditioner?

No, use it only as a rough guide; a proper load calculation should confirm the size before purchase.

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