BTU Calculator

Find your perfect radiator

Correctly calculate your BTU requirements to -

  • Create warm & inviting rooms
  • Increase the efficiency of your heating
  • Take control of your fuel bills

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What size radiator do I need?

We recommend choosing a radiator size that is within a 10% range of your calculated BTU requirement. If it’s a choice between buying a radiator that is too small, versus buying one that is too big, it’s always best to buy one that is too large and oversize the radiator. You can always turn a bigger radiator down, but you can’t make a smaller radiator give out more heat!

How do I choose the right radiator?

BTUs are ‘British Thermal Units’, the unit in which radiator efficiency is measured. Factors such as room dimensions, window size and wall material are used to calculate the required outputs of radiators, in order to adequately heat a room.

Use our BTU Calculator to determine the heat requirements of your room. Simply enter the details in the corresponding fields and we’ll show you how many BTUs you need to ensure your space is always warm, cosy and inviting.

How do I calculate the BTUs for my room?

The best way to get an accurate calculation is to enlist the services of a plumber. However, BestHeating's BTU calculator is a good guide as to what level of BTU and Watt output will efficiently heat your room. Please note: the calculated figure is for the combined heat output of all radiators and/or towel rails in your room (larger rooms may require more than one).

Calculate the required BTU output of your room

Room Dimensions

Width (m) *
Height (m) *
Length (m) *
Window Area X² (Calculate this by multiplying window height by window length): *
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

Type of room: *
Where are you heating?
What is below the room? *
Think about the flooring of your room, and whether there is another room below
What is above the room? *
Where applicable, choose the amount of insulation
Select type of outside wall: *
This helps us calculate how much heat the room might lose
Select type of window: *
This also helps us determine the expected heat loss in the space
Select number of outside walls: *