Home Improvement
AC size calculator
Air conditioners are sized by heat load: the number of BTU per hour the room adds on a hot day. Enter the room's area, ceiling height, sun exposure, insulation, and how many people use it, and the calculator applies the standard adjustments to the 20 BTU per square foot baseline. The result converts to tons and points at the next unit size you can actually buy — so you neither undersize a room into misery nor oversize it into a clammy, short-cycling machine.
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AC Size Calculator
Work out the cooling load in BTU and the air conditioner size a room actually needs.
Inputs used
Results
The heat the room adds on a hot day.
Additional notes
Your estimate
Results
The heat the room adds on a hot day.
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Window air conditionerYour BTU is set — pick the unit that matches it.Paid link · Check current price ↗As an Amazon Associate I earn from qualifying purchases.The math, plainly
How it works
- 01
Start from 20 BTU per square foot of floor space — the standard room-cooling baseline.
- 02
Scale for ceiling height, sun, and insulation, then add 600 BTU per person beyond two and 4,000 BTU for a kitchen.
- 03
The load converts to tons (12,000 BTU per ton) and rounds up to the next unit size you can actually buy.
Try a real scenario
Sunny kitchen, 3 people
Inputs300 sq ft, 8 ft ceilings, very sunny, kitchen, 3 people
ResultAbout 11,200 BTU (0.9 tons) — buy a 12,000 BTU (1-ton) unit.
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More options for this calculator
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Quieter and more efficient than a window unit for rooms you cool daily.
Smart thermostat (paid link)
Schedules and setbacks that shave the bill without sacrificing comfort.
Caulk & weatherstripping (paid link)
Sealing leaks cuts the load itself — the cheapest BTU you will ever buy.
As an Amazon Associate I earn from qualifying purchases.