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  • Measure the length and width of the room and multiply the figures to determine the square feet.
  • Multiply the result in step one by 25.
  • For each occupant in the room, add 400. For example, in a couple's bedroom, the total would be 800. Add this to your total from above.
  • Add 1,000 for each window in the room.
  • The total should give you a rough estimate of the amount of BTUs needed to cool the room and keep it at a comfortable temperature.

Radiator BTU Calculator

The efficiency of radiators, old and new, is measured in British Thermal Units (BTU).
The dimensions of a room are used to calculate the amount of BTU needed to heat that room.
Radiators all have a known and calculated BTU output.
Using the BTU outputs it is easy to calculate the size of radiator you need to heat your room.


Please Enter The Dimensions Of Your Room

Width (ft)

Length (ft):  

Height (ft): 

What Type Of Room Is It?

Dining Room/Lounge/Bathroom


Kitchen / Common Area

Other Factors

Does the room face North?


Does it have French windows?


Does it have Double Glazing?


 Press Here to Calculate