Underfloor Heating Mat Calculator — What Size Mat Do I Need?

This calculator determines the correct electric underfloor heating mat size by calculating the heated floor area (total area minus fixed furniture), then matching it to the nearest standard mat that still fits, and working out the electrical requirements.

The formulas

Heated area = Room area × (1 − Fixed furniture %)
Mat size = Largest standard size ≤ heated area (round DOWN — the cable can’t be cut, so the mat must fit)
Total wattage = Mat size × W/m²
Amps = Wattage ÷ 230V

Wattage guidelines

• 200W/m²: Most bathrooms and high heat-loss rooms (conservatory, garden room, older/poorly insulated property, large glazing, or where >20% of the floor is excluded by fixtures) — faster warm-up, sole-heat-source capable
• 150W/m²: Well-insulated living rooms, kitchens and hallways — comfort or supplementary heating

Electrical requirements

• Up to 3.6kW (16A): Standard 2.5mm² circuit with 16A MCB + 30mA RCD
• Over 3.6kW: Requires contactor or multiple circuits — consult electrician
• All UFH installations require 30mA RCD protection
• Floor probe sensor thermostat is essential