BTU Calculator
Calculate BTUs needed to heat or cool a room.
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How It Works
Calculates the BTU (British Thermal Units) required to heat or cool a space. Rule of thumb: 20 BTU per square foot. Adjust for ceiling height, sun exposure, insulation, and climate.
Formula
BTU = Area x 25 (standard)Quick Reference
Common calculations — results you can verify instantly.
500 sq ft room
500×20 BTU
10,000 BTU/hr
1,000 sq ft
1000×20 BTU
20,000 BTU (1.67 tons)
1 ton cooling
Standard unit
12,000 BTU/hr
Tips & Shortcuts
Add 10% for very sunny rooms.
Subtract 10% for heavily shaded rooms.
1 ton of AC = 12,000 BTU/hr. A 1,500 sq ft home typically needs 2-3 tons (24,000-36,000 BTU).
Common Mistakes
Sizing AC only by square footage without considering ceiling height
High ceilings dramatically increase the volume to cool. A 10ft ceiling needs 25% more BTU than an 8ft ceiling.
Assuming bigger is always better for AC
Oversized AC cools too fast without dehumidifying properly, causing clammy air and short-cycling that wastes energy.
Frequently Asked Questions
Approximately 10,000 BTU for standard 8ft ceilings. Adjust up for sunny exposure or down for shaded areas.
12,000 BTU/hr — the amount of cooling needed to melt 1 ton of ice in 24 hours. A common residential unit is 1.5-5 tons.
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