How to Measure How Many BTUs to Heat a Room

Written by steve sloane
  • Share
  • Tweet
  • Share
  • Pin
  • Email
How to Measure How Many BTUs to Heat a Room
Measure the room's length, width and height to calculate its BTU requirement. (tape measure image by Joann Cooper from

A BTU (British Thermal Unit) is a measure of heat energy. One of these units signifies how much energy it will take to heat one lb. (473ml.) of water one degree Fahrenheit hotter than it is already (for example, heating 0.454kg. of water form 18.3 to 18.9 degrees Celsius). Household room heaters come in different BTU sizes, with the required BTU for a room being determined by multiplying the room's volume by its quality of wall/floor/ceiling insulation.

Skill level:

Other People Are Reading

Things you need

  • Tape measure
  • Calculator

Show MoreHide


  1. 1

    Measure both the length, width and height of the room that needs to be heated (measure in feet and inches).

  2. 2

    Multiply these three measurements together. This calculation will give you the room's cubic volume.

  3. 3

    Rate the room's insulation in the walls, ceiling and floor. If the insulation is very good, give it a No. 2 rating. If the insulation is medium quality, give it a No. 3 rating. If the insulation is poor, give it a No. 4 rating.

  4. 4

    Multiply the room's calculated volume by its insulation rating. This number will give you the number of BTU's required to heat the room.

Tips and warnings

  • It is best to error on the side of caution when choosing the correct size heater for a room. For example, if the calculation for the room comes to 15,000 BTU's, and the heater you are purchasing comes in 15,000 and 20,000 BTU , it is best to choose the 20,000 BTU heater. This is especially so in colder or wetter climates.

Don't Miss

  • All types
  • Articles
  • Slideshows
  • Videos
  • Most relevant
  • Most popular
  • Most recent

No articles available

No slideshows available

No videos available

By using the site, you consent to the use of cookies. For more information, please see our Cookie policy.