Radiator Heat Output Calculator
This radiator calculator (also known as a heat loss calculator) will provide a guide to the output required both in BTUs and Watts, for a specified room.
The calculator requires measurements to be entered in metres so we've included a handy imperial to metric converter if required - simply enter your dimensions in feet and inches (or just inches) and click the CALCULATE button.
The main radiator calculator is easy to use - just complete the form including room dimensions, window area (multiply height x width of window frame) and select the floor, ceiling and wall details that best match your home. The results are given at the bottom of the page and include BTU (British Thermal Units) and Watts for your convenience.
Feet & Inches » Metres Converter
View our full range of radiators by selecting the type below.
What size radiator do I need?
The calculator works out the heat output requirement and now we've added dynamic links which will appear once you've entered your room size etc. The links will take you to a selection of radiators based on your heat output results enabling you to buy right away if you like! There's Standard Radiators, Designer Rads, Traditional Style Column Radiators plus Heated Towel Ladder Rails in both Classic and Modern Designs.
Please note that this radiator calculator uses industry standard formulas, however, the results are for guidance only and we make no guarantees as to the accuracy of individual results. You may find some online radiator calculators provide differing results - our advice would be to go with your gut instinct and apply common sense. A higher result means you will be looking for a larger radiator which happens to cost more...
We hope the information provided is of interest and that it helps you make an informed choice of radiator. We would welcome any comments you may have - please send emails to or call on 01752 705522.