Radiator Calculator

Need to find what radiator size I need? Use our calculator to estimate radiator size and find the required BTU/Watts output for the best room heating.

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Why do I need a radiator size calculator?

When buying a heating radiator for the house, many face the problem of choosing a size. It is important to pay attention to this, because the wrong size radiator can make the room too cold or too hot, the air too wet or too dry.

Our tool allows you to estimate the size of the heating radiator by room size, heating rate or heat loss. To perform the calculation, you will need to determine the length/width/height of the room, check with the manufacturer for the capacity of one radiator section, and select the type of connection. Please note that a 10-15% power reserve is recommended. The theoretical justification for the calculation is below.


Radiator size formulas

Radiator size can be calculated in two ways: by room volume or by heat loss.

The formula for the first case:

k = (V × q × z) / P2

  • V – room volume, m3;
  • q – heating rate, W/m3;
  • z – correction for connection type;
  • P2 – heat output of one radiator section, W.

Correction values based on the type of connection:

  • single-sided (bottom input / top return) – 1.28;
  • single-sided (top input / bottom return) – 1.03;
  • double-sided (input-return from one side) – 1.28;
  • diagonal (bottom input / top return) – 1.00;
  • diagonal (top input / bottom return) – 1.25.

The second version of the calculation is based on the fact that the radiator size is determined depending on the heat loss of the room.

k = Q / P2

  • Q – heat loss room, W;
  • P2 – heat output of one radiator section, W.


Heat output of one radiator section

Материал радиатораHeat output of one section, W
Hub distance, 300 mmHub distance, 500 mm
Cast iron100160
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