BTU Calculator (AC Heater Sizing)
AC or heater BTU needed for any room
Recommended size
—
BTU/h
≈ — kW · — tons
📚 Learn more — how it works, FAQ & guide Click to expand
Learn more — how it works, FAQ & guide
Click to expand
Free BTU calculator — AC and heater sizing
Size your AC or heater correctly. Oversizing wastes energy; undersizing fails to cool/heat.
How to use this tool
- 1
Enter room dimensions
Length, width, ceiling height in feet or meters.
- 2
Pick climate + insulation
Factors affect BTU needs significantly.
- 3
Get AC/heater size
Round up to nearest standard size.
Frequently Asked Questions
Oversizing AC?
Bad idea. Oversized AC cools too fast, doesn't dehumidify, short-cycles (wear). Aim for 10-15% above calculated.
Base formula
Sq ft × 20 BTU = baseline. Adjust for sun, insulation, occupants, climate.
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100% Privacy. This tool runs entirely in your browser. Your data is never uploaded to any server.