BTU Calculator

A British Thermal Unit (BTU) is a measure of heat output from a radiator. Depending on the size of your room, the number and type of windows and what the room is used for, you'll need more or less heat. If you have a higher BTU requirement, it might be better to use more than one radiator to deliver the heat you'll need to a room. The total BTU output of several smaller radiators may meet your needs.



  Length Width Height



Room Type?


Does the room have?

  French Windows  
    North Facing Walls  
    Double Glazing  
  Required BTU Watts

This calculator will give an approximate value of the BTU/Watts required for your room. There are various factors which can and will affect the output required. for a more precise calculation please seek professional advice.


If you're measuring your room in metres then measure to the nearest centimetre. Enter your measurments using decimal notation for example 425cm would be entered as 4.25m.

When it comes to measuring the height if you have a vaulted or sloping ceiling use an average.


For example a room measuring 4 x 3 x 2.5 metres simply enter the measurements then set the room type. Tick the relavent boxes for French windows, North facing walls or double glazing. Then click the submit button.

So if our room was a bedroom measuring 4 x 3 x 2.5 metres and has double galzing then this gives results of 3811 BTU and 1117 Watts.


Please call us on 01663 749027 for advice.

Delta T 50 ° Converter

If you have been looking at radiators for any length of time you may have noticed the term ‘Delta T’. Delta T is a rating of the heating system.

It is calculated by the following method. Take an average of the following:

Temperature of the water going into the radiator °C

Temperature of the water coming out of the radiator °C

Then deduct the room temperature of 20°C


The European Union standard is Delta T 50. Radiator manufactures in the UK should be using this standard. Some suppliers are not using this standard as a way of inflating the heat outputs of their radiators.


To use this converter simply enter the BTU value for the radiator and select the Delta T value in the drop down.

For example, if you have a brochure showing a radiator rated at 3996 BTU Delta T 70, then enter 3996 in the BTU field and change the selector to 70. In Delta T 50 that should give 2850.

  BTU Watts Delta T
BTU or Watts
The value in Delta T 50 ° is BTU which is Watts

Press F5 or refresh the page to clear the boxes.