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.
Live calculator
Enter your details
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.Check current price ↗As an Amazon Associate, CalcForged earns 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.
Gear for the job
Tools & materials people actually buy
Window air conditioner
The standard fix for one room — match the BTU rating to your load.
Mini-split system
Quieter and more efficient than a window unit for rooms you cool daily.
Smart thermostat
Schedules and setbacks that shave the bill without sacrificing comfort.
Caulk & weatherstripping
Sealing leaks cuts the load itself — the cheapest BTU you will ever buy.
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