BTU Calculator

Estimate the cooling or heating needs of a room or house. Finding the correct BTU rating for your Air Conditioner or Heater ensures maximum comfort and energy efficiency.

Room Dimensions & Occupancy

Room Size (sq ft)

Ceiling Height (feet)

Number of People Inside

Room Type

Environmental Factors

Insulation Quality

Sun Exposure

Results

3,375

Required BTUs

AC Tonnage0.28 Tons1 Ton = 12,000 BTU

Comprehensive Guide to BTU & HVAC Sizing

What is a BTU?

BTU stands for British Thermal Unit. It is a traditional unit of heat defined as the amount of energy required to raise the temperature of one pound of water by one degree Fahrenheit. In the HVAC (Heating, Ventilation, and Air Conditioning) industry, BTU actually refers to BTU per hour (BTU/h)—the cooling or heating capacity a machine can deliver within an hour.

What is an "AC Ton"?

When you look at central air conditioning units, you will often see them rated in "Tons" rather than BTUs. This is a historical term originating from the days before mechanical refrigeration, when buildings were cooled using actual blocks of ice harvested in the winter.

1 AC Ton = 12,000 BTU/h

It takes exactly 288,000 BTUs to melt one ton (2,000 lbs) of ice in 24 hours. If you divide 288,000 by 24 hours, you get exactly 12,000 BTUs per hour! Therefore, a "2-Ton AC unit" has a capacity of 24,000 BTU/h.

General Rule of Thumb (Energy Star Guidelines)

While our calculator provides a highly tailored estimate based on your specific environmental factors, the US Department of Energy (Energy Star) provides this baseline chart for standard 8-foot ceiling rooms:

100 - 150 sq ft
5,000 BTU

150 - 250 sq ft
6,000 BTU

250 - 300 sq ft
7,000 BTU

300 - 350 sq ft
8,000 BTU

350 - 400 sq ft
9,000 BTU

400 - 450 sq ft
10,000 BTU

450 - 550 sq ft
12,000 BTU

550 - 700 sq ft
14,000 BTU

The Danger of Oversizing & Undersizing

❌ Oversized (Too Many BTUs)

An oversized AC cools the room down extremely quickly and then shuts off. Because the cooling cycle is so short ("short cycling"), the unit fails to extract humidity from the air. The room will reach the target temperature, but it will feel damp, "clammy", and uncomfortable. It also increases wear and tear on the compressor.

❌ Undersized (Too Few BTUs)

An undersized unit will run constantly without ever reaching the desired temperature on a hot day. This continuous operation consumes massive amounts of electricity and will eventually cause the machine's motor to overheat and burn out prematurely.