BTU Calculator

Use our BTU calculator to easily work out what size radiator you will need, by entering information about your room in our calculator.

What size radiator do I need?

Before making a purchase, it’s important that you use a radiator calculator to work out what size radiator you will need to heat your chosen room. If you don’t do this, you may find your radiator is too weak or too powerful for your requirements. 

In order to work this out, you need to calculate the BTU as well as the watts required to heat it effectively.

How to calculate BTU for a room

In order to calculate your BTU output that is required, you will need to measure the length, width, and height of your room. You can use our radiator BTU calculator below to enter this information, as well as the type of room, type of window glazing, and how sheltered or exposed it is.

Give your room a name, so you can save it to your Wishlist for easy reference.

Please note: this is a guide only
A radiator with insufficient output may never raise the temperature to the required level. Outdoor temperatures, external walls, insulation, heated adjacent rooms (i.e. above, below, and to the side) all have a contributing effect. The boiler should have sufficient capacity to supply all connected radiators to the sum of their maximum demand. Larger rooms such as living rooms may require more than one radiator, positioned evenly throughout the room. If this is the case, simply divide the required output between the number of radiators needed.

What does BTU stand for?

BTU stands for British Thermal Unit.

What is BTU?

The British Thermal Unit  is the amount of heat needed to increase the temperature of one pound of water by one degree Fahrenheit.

What does BTU mean in relation to radiators?

With radiators, the BTU measurement refers to how much energy is required to heat a particular room. The higher the BTU number is, the greater the radiator’s heat output will be. How effective the radiator will be though depends on factors such as the size of the room and how insulated it is.

What is BTU? The BTU rate of a radiator is how much heat the radiator will emit, and is there to help you decide if a radiator is the correct size for your room or not. It’s important to know how much heat your room needs in order for your system to work efficiently.