BTU Calculator

Work out the heat requirements of any room with our handy BTU calculator.

What Is BTU?

BTU stands for British Thermal Unit and, when shopping for radiators, refers to the amount of energy required to effectively heat a room. Whether you’re warming up a small en-suite or a large commercial office, you’ll need to find a radiator (or several radiators) with a BTU output that meets your room’s requirements.


In general, small rooms will need radiators with a lower BTU output, whilst larger rooms will need a higher BTU output – but there’s a lot more that goes into it than that!

What Impacts BTU?

A number of things can impact the BTU requirement of a room, including:

Windows – single or double glazed, the size, and how many of them.

The number of outside walls.

The size of the room.

Whether the room is on or above the ground floor.

How To Use The BTU Calculator

Unsure of how many BTUs you need for your room? Our handy BTU calculator has you covered!


Simply measure the height, width and length of the room in question in metres or feet. Then, measure the size of your windows in m².


Next, fill in details about what’s above and below the room (i.e. if it’s a room on the second floor, there’ll be another heated room below).


Finally, clarify whether the windows are single or double glazed and the frame around them – and the number of outside walls in the room.


Once you know the BTU output required for your room, our radiator buying guide will help you find the perfect size, style and type of radiator for your space.

BTU Calculator

What type of room are you heating?

What are the room dimensions?

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