Radiator Sizing Calculator

Keep your rooms warm by working out radiator sizes in kW or BTU

Radiator Sizing Calculator Tool (BTU and KW)

Radiator size calculator to help you work out how many BTU or KW you need your radiators to output to keep your house nice and warm. This size calculator will help you work out the BTU or kW sizes of your radiators with no need for complex charts or heating graphs!

Just choose the number of rooms you want to calculate sizes for, enter the room dimensions, choose whether you want a simple calculation or a more advanced version, select a standard ceiling height for your rooms (you can change this later) then hit the button. The required radiator heat outputs (in kW and BTU) are worked out for you

Free Radiator Sizing Calculator

How Many Rooms:
Standard Ceiling Height:

Working out the correct KW or BTU heat output of your radiators is probably the most important step in specifying a central heating system. This radiator size calculator will give you a good starting point although you may wish to consult a heating engineer who can perform a more detailed calculation

Alternatively you could use this as a check for the radiator BTU or KW outputs that your engineer has specified.

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Calculating Radiator Sizes Top Tips

Bathroom Towel Radiators

Towel radiators give notoriously poor heat output when they are loaded up with towels or drying washing so it maybe be best to have another radiator or heat source in bathrooms

Room Comfortable Temparature

If you like your rooms especially warm it may be better to oversize your radiators slightly. Ultimately, if they are too big you can just turn them down a bit, but if they are too small there's not much you can do

Converting BTU to KWh

use our handy BTU to KW Convertor to convert figures from BTU to KWh