Find the right warmth
for your room
Our BTU calculator helps you find the perfect heating solution for your space. By working out the heat your room actually needs, you can avoid overspending on oversized radiators or ending up with one that simply can't keep the room warm.
and easy to use
BTU estimate
the right radiator
1. Which room would you like to heat?
Choose the room type to help us estimate your heating needs.
2. What are the dimensions of the room?
Choose an estimated room size or enter your own dimensions for a more accurate calculation.
3. How exposed is the room?
Rooms with more external walls or less shelter need more heat.
4. What window type do you have?
Double glazing keeps more heat in than single glazing.
Please enter a valid room width, length and height.
Enter your room details and calculate to see your result.
Find your perfect radiator
Now you have your estimated heat requirement, explore our radiator range to find the ideal size and style for your room.
Shop radiatorsFrequently asked questions
What does BTU stand for?
BTU means British Thermal Unit. Radiator heat output is usually expressed in BTU per hour (BTU/hr).
What does Delta-T 50°C mean?
Delta-T 50°C describes a standard radiator output rating condition, where the average radiator water temperature is 50°C above the room temperature. Actual output changes with your heating system's operating temperatures.
What if my BTU figure is very high?
You can consider multiple radiators, provided their combined heat output meets the estimated requirement. Improving insulation and reducing draughts can also help.
What if I'm planning multiple radiators?
Divide the room's total estimated BTU requirement across the radiators. Their combined rated output should meet the requirement at the temperatures your heating system uses.
This calculator provides an indicative estimate using room volume and broad adjustment factors, not a professional heat-loss calculation. Insulation, ventilation, outdoor design temperatures and heating-system operating temperatures can materially affect the required output.