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BTU Calculator

Have you ever wondered how to work out the perfectly sized radiator for each specific room in your house? Well wonder no more, as UK Radiators’ BTU calculator does just that.

What is a BTU?

BTU (British Thermal Unit) measures the appropriate amount of energy your radiators need to properly heat any room of your house.

A specific radiator's heat output is measured in BTUs to work out the amount of energy required to heat one pound of water by one degree Fahrenheit. This gives you an indication of how many BTUs are required to heat a room, and in turn the specific radiator size that is required. 

What is a BTU calculator?

BTU calculators are a great tool for working out how much energy you’ll need to efficiently heat up a room. Calculating the BTU for each room size is essential for maintaining energy efficiency in your home. It is important to carefully consider each radiator’s size to provide the appropriate heating for each room and cope with its insulation demands.

Fitting in inaccurately sized radiators to a room can cause insulating problems as it won’t meet the heating demands of the required space. That’s why it is important to use a BTU calculator and accurately work out the number of BTUs needed to heat each room in your home.

How to calculate BTUs

When it comes to calculating the BTUs needed for a specific room, there are two main factors to keep in mind. 

Firstly, you need to decide at which temperature you would like to maintain each room. Pretty simple, right?

Secondly, you need to consider the heat loss from a room as this directly affects the constant level of temperature maintained in the space. 

There are several factors that affect the heat loss of a room; its size, the number of windows and their insulating properties (single or double glazed), what is surrounding the room, and the number of internal and external walls. 

Taking all these factors into consideration can seem a bit complicated, but the general radiator sizing rule of thumb is, the bigger the size of the room, the more BTUs are required to maintain a consistent and comfortable temperature.   

Calculate BTU for a room size 

You can accurately measure the required BTUs for any room size by simply entering the required information into the calculator below, making sure the measurements given are as accurate and concise as possible. 

The results will show the required total number of BTUs needed to keep that room size at a consistent temperature. You may need more than one fitted radiator to keep the constant and comfortable temperature required. 

Here at UK Radiators we have a wide range of radiators to suit your heating needs and they come in all shapes and sizes to keep your room warmer for longer. Get in touch today to get a perfectly sized radiator for each room in your home, saving you energy costs and trouble!


Fill out the form below with the details of your room and let our BTU Calculator do the rest for you.

Type of room:

Room Dimensions

What is below the room?

What is above the room?

Type of windows:

Type of outside walls:

Number of outside walls:

Total Required Output

( Watts)
* = Delta T value

We can help you to decide on the right radiators for your property, contact us for more information.