BTU Calculator


Calculate your bathroom BTU requirements to:

  • Create an inviting bathroom space
  • Improve heating efficiency
  • Positively impact fuel bills

How do I choose the right bathroom radiator?

A BTU is a "British Thermal Unit" and it is the unit by which to measure your bathroom radiator's efficiency. As with any other room of your home, to accurately heat your bathroom space, you must consider factors such as wall materials, window size and room dimensions. You can use our BTU Calculator to work out the heating requirements of any room. Simply enter the measurement details and other information into the fields below, and we'll let you know just how many BTUs you may need to heat your room efficiently.

How do I calculate BTUs for rooms in my home?

The best and most accurate way to get our BTU calculation is to ask your local plumber. That said, the Big Bathroom Shop BTU calculator can offer a good guideline for the level of heat output you need to adequately heat your chosen room. Please note: The figure that is calculated will be for the combined output of all radiators/towel rails in the room and some larger spaces may require more than one appliance.

Calculate your BTUs

Room Dimensions

Width (m) *
Height (m) *
Length (m) *
Window Area X² (Multiply height by width): *
If your room does not have a window, please enter '0' in the field below & select 'no window' in the relevant field below

Room Information

Room type: *
Which space are you heating?
What is below the room? *
Is there a room below? What type of flooring is it?
What is over and above the room? *
Another heated space? Insulation? Where appropriate choose insulation type.
Choose the type of external wall: *
This can help calculate the heat loss of a room
Choose window type: *
This also helps understand a room’s heat loss
How many external walls? *