Heater size calculator
Enter the room size and ceiling height. You’ll get the heater power to look for and how many 2 kW heaters that takes.
Measuring in feet and inches? Use the US version
Heater size
1,400 watts
- In kilowatts
- 1.4 kW
- 2 kW heaters
- 1
- Room size
- 14 m²
How it works
A common rule of thumb for electric heating is about 100 watts per square metre of floor in a room with a 2.4 m ceiling. The calculator scales that for taller or lower ceilings, and by 20–25% for insulation that’s better or worse than average.
Example
With room length 4 m, room width 3.5 m, ceiling height 2.4 m, insulation: average, the answer is 1,400 watts.
Tips before you buy
- If the heater is topping up a room that already gets some central heating, you can go smaller.
- Rooms with large windows, several outside walls or a floor over an unheated garage need the higher end.
- Most plug-in heaters top out at 2 to 3 kW. Bigger rooms need more than one, on separate sockets.
Common questions
What size heater do I need for a 4 × 3.5 m room?
About 1.4 kW with a 2.4 m ceiling and average insulation, so one 2 kW heater.
How many square metres will a 2 kW heater heat?
About 20 m² as the main heat source, by the 100 watts per square metre rule.
How many watts per square metre do I need?
Around 100 W/m² for an average room, 80 for a well-insulated one, and 125 or more for an older, draughty room.