SITE TOOLS // RADIATOR SIZING ESTIMATOR
Radiator BTU Calculator
Work out roughly what size radiator a room needs – enter your measurements below.
ABOUT THIS CALCULATOR
Undersizing a radiator means a room that never quite gets warm; oversizing wastes money and overheats the space. Getting the BTU output right depends on more than just floor area – room type, insulation quality and the number of external walls all change the real heat loss.
This calculator uses standard UK heat loss rates by room type – kitchens typically need less heating input than bathrooms, for example, because appliance heat and usage patterns differ – combined with adjustments for insulation and exposure, plus a 15% safety margin in line with common heating engineer practice.
It’s a solid starting estimate; for anything beyond a straightforward domestic room, a full heat loss survey is worth getting before ordering a radiator.
M
M
M
Recommended Output
0 BTU/h
0 Watts, including a 15% safety margin
Sizing the job as well as the radiator? PlumberLog turns the job into a quote and tracks it through to invoice.
Try PlumberLog Free
This is a simplified estimate for guidance only, based on typical UK room heat loss rates. Glazing type, floor level, radiator position and exact insulation values all affect the real figure – for anything beyond a rough guide, get a proper heat loss calculation from a qualified installer.