calculator symbols

BTU Calculator

Please enter your information below:

Length (m) *
Width (m) *
Height (m) *
Window Area X² (m) (Multiply height by width): *
If your room does not have a window, please enter '0' in the field below & select 'no window' in the relevant field below
Choose window type: *
This also helps understand a room’s heat loss
Room type: *
Which space are you heating?
What is below the room? *
Is there a room below? What type of flooring is it?
What is over and above the room? *
Another heated space? Insulation? Where appropriate choose insulation type.
Choose the type of external wall: *
This can help calculate the heat loss of a room
How many external walls? *
Your Requirements
Watts Required
  • Measurement:
  • Length: m
  • Width: m
  • Height: m
  • Window Area X²: m
  • Room type:
  • What is below the room?:
  • What is over and above the room?:
  • Choose the type of external wall:
  • Choose window type:
  • How many external walls?:
BTU's Required

What are BTUs?

British Thermal Units (BTUs) are a unit of measurement by which the heat output of radiators can be determined. A BTU is approximately the energy required to heat 1lb of water from 39°F to 40°F. The heat output of radiators and towel warmers is often given in the form of BTUs, which allows homeowners to be sure that the products they are buying will supply enough heat.

What are Watts?

Watts are an alternative unit of measurement for heat output, and the wattage required to effectively heat a room is determined by factors such as its dimensions, the size of its windows and the material from which its walls are built. Watts can also be easily converted to BTUs (1 W = 3.412142 BTU/hr).

How do I calculate Watts for my room?

The Hudson Reed wattage calculator can provide you with an accurate assessment of how many watts are required to adequately heat your room. For the most accurate calculation you may need to contact a professional plumber. Please note that the figure calculated is the required output of all radiators and towel warmers in the room (larger rooms may require more than one radiator).