Before replacing or adding a radiator, this calculator gives the power you need from the room volume, insulation quality and climate zone. An undersized radiator never heats properly, an oversized one wastes energy.
Methodology
This calculator produces an indicative estimate based on the parameters you enter. The ranges used reflect typical market tiers in the eco and energy savings space and are neither a commercial offer nor a guarantee. Prices and availability may vary.
Prices and availability may vary. As an Amazon Associate we earn from qualifying purchases.
All our calculators you can embed →
Frequently asked questions
How many watts for a 12 m² bedroom?
Expect about 1,200 W with average insulation in a temperate climate (12 m² × 2.5 m × 40 W/m³). Add 25% if insulation is poor, take off 25% if it is recent.
Why watts per m³ rather than per m²?
Because ceiling height changes everything: a 20 m² room under 2.5 m needs less energy than the same floor area under 3.2 m. Volume-based sizing stays correct in both cases.
Should I add a safety margin?
Not usually, unless the room is very cold or poorly insulated: better to choose a model with several power levels or a programmable thermostat than to oversize it.