How many BTU do I need for a room air conditioner?

A quick estimate starts around 20 BTU/hr per square foot, then adjusts for sun exposure, ceiling height, insulation, people and equipment heat.

What happens if an AC is too large?

It can short-cycle, run noisier, remove less humidity and create uneven comfort.

Is AC BTU the same as electricity use?

No. BTU/hr is cooling capacity. Electricity use depends on the unit's efficiency, runtime and operating conditions.

Air Conditioner BTU Calculator

Estimate room air conditioner size in BTU/hr from square footage, ceiling height, sun exposure, insulation, occupants and equipment heat.

Cooling load estimate

Estimate room air-conditioner capacity in BTU/hr from square footage, ceiling height, sun exposure, insulation, occupants and simultaneous equipment heat.

Room area, sq ft

Ceiling height, ft

Sun exposure

Insulation

Regular occupants

Equipment heat, BTU/hr

Enter the simultaneous average heat load for computers, kitchen appliances or other equipment.

Common room AC sizes

5,000 BTU/hr100-150 sq ft

6,000 BTU/hr150-250 sq ft

8,000 BTU/hr300-350 sq ft

10,000 BTU/hr400-450 sq ft

12,000 BTU/hr450-550 sq ft

18,000 BTU/hr700-1,000 sq ft

Estimate room AC size

English AC-sizing intent is usually room-oriented: square footage first, then adjustments for sun, ceiling height, insulation, people and appliance heat. The result should be in BTU/hr with a common room air-conditioner size.

Q_{ba se} = A_{f t^{2}} \cdot 20

Qbase - base cooling load in BTU/hr for a room estimate.

Q_{coo l} = Q_{ba se} \cdot F_{s u n} \cdot F_{in s u l a t i o n} \cdot F_{h e i g h t} + Q_{p eo pl e} + Q_{e q u i p m e n t}

Qcool - adjusted cooling load.

1 t o n = 12, 000 B T U / h r

Tons are common for larger AC and heat-pump equipment.

Avoid oversizing

Oversized room air conditioners can cycle off too quickly and remove less humidity.
Very sunny rooms, kitchens, top floors and poor insulation can need more capacity.
Open floor plans and central systems need a load calculation, not only a room-size chart.
Cooling capacity is different from electrical consumption.

Estimate only

Use this as a quick room AC estimate. Central AC, heat pumps and unusual rooms need a qualified Manual J or equivalent cooling load calculation.

Frequently Asked Questions

Sources and References

Calculations are based on the listed reference sources. Links open in a new tab.

Updated: June 2, 2026

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