How Many BTUs For Air Conditioners Do I Need?

Coby McKinley Profile image

Written By:

Updated August 12, 2022

With so many options to choose from, finding the best air conditioners can be hard. Central air conditioners are scaled to fit the rooms they cool. Portable air conditioners are convenient so long as you know how long to cool a room with a portable A/C. Knowing this, you’ll discover how many watts a portable A/C uses. And choosing from among the variety of window air conditioners is easy when you know how to find the right size for your needs. To do that, you need to know the standard BTU calculation.


  • The EPA recommends 20 BTU per square foot as a rule of thumb
  • Kitchens may require more BTUs than suggested by their square footage
  • Factors like ceiling height, body heat, poor insulation, and sun exposure will affect the size unit a room needs.

Calculating BTU

To buy the proper size air conditioner for your room, you must first determine the space’s square footage. Not every portable air conditioner is built to cool all areas. It’s important to find the right unit size for your space, because it doesn’t mean that the weight of a window air conditioner equates to more power. And, it won’t only narrow down your cooling options, but it ensures you buy an ac with enough cooling capacity. The formula is simple and can help you find how many BTU for a window AC or portable ac.

Insider Tip

There are many types of air conditioners. Consider all options to ensure you choose the best choice for your needs.


If using a layout of the room, use the numbers on the diagram. Otherwise, measure the length and width of the room, as well as the height from floor to ceiling.


Multiply length times width times height to find the number of square feet in a space.


Multiply the total from step 2 by 20, as the EPA suggests an appropriately sized unit will need 20 BTUs for every square foot.


Compare your final number with an air conditioner BTU chart to find the capacity needed for your room.


Always properly secure window ACs, so they do not fall on anyone below


How are central air conditioners measured?

BTU stands for British Thermal Unit. A cooling unit’s output is measured in BTU/h or BTUs per hour when measuring a cooling unit’s capacity.

What else should I look for when buying a room air conditioner?

Before committing to a specific unit, you may also want to consider energy efficiency and ENERGY STAR products, operating costs, and a company’s return policy. Also, ACs are expensive when using standard shipping as they are heavy products. Don’t forget to factor in shipping, especially if you opt for faster home delivery.

Will an air conditioner with a higher BTU cool my room faster?

No. Higher BTUs or more powerful units will not reach a comfortable temperature faster. The higher number only means that the unit is rated to cool a larger space. Though if you’re cooling a kitchen, you should consider the heat load given off when cooking and purchase a unit with additional BTUs

How do I measure the square footage of a room?

To take an accurate measurement, ask someone to hold one end of the tape measure while you use it to determine the length, width, and height. Then follow the above steps to find the square footage and BTU needs.

STAT: Air conditioners use about 6% of all the electricity produced in the United States, at an annual cost of about $29 billion to homeowners. (source)

Coby McKinley Profile image