Underfloor Heating Cable Calculator

How to use this calculator

1. Enter the heated floor area (the free area, excluding fixed furniture and fittings).
2. Choose the target output in W/m² and the cable rating in W/m.
3. Click Calculate cable for the power, cable length and spacing.

How the cable length and spacing work

The floor power is the area times the watt density; the cable length is that power divided by the cable's rating per metre; the center-to-center (C-C) spacing follows from spreading that length over the area:

A heating cable is supplied at a fixed length and must not be cut, so choose a kit whose length is close to the calculated value.

Output by floor finish

A 10 W/m cable suits ~100 W/m² installs at ~10 cm spacing; 17 W/m cable covers larger areas with wider spacing.

Frequently asked questions

How long a heating cable do I need?

Multiply the heated area by the target W/m² to get watts, then divide by the cable's W/m rating. For example, 5 m² at 100 W/m² is 500 W; with a 10 W/m cable that is 50 m.

What spacing should the cable have?

Center-to-center spacing equals the heated area divided by the cable length, in metres, times 100 for centimetres. Typical floor cables sit at 8–12 cm spacing.

Can I cut a heating cable to length?

No. Resistance heating cables are a fixed length and cannot be shortened. Pick a cable or mat whose length matches your area, or adjust the spacing slightly.