Heated Floor Calculator

Mat sizing and thermostat for electric radiant floor.

Room area

sq ft

Fixtures / cabinets

Watts per sq ft

W/sqft

Daily run time

hrs

Electricity rate

$/kWh

Mat width

Tab to move between fields

Heated area

96 sq ft

≈ 2 king-size beds

Thermostats needed

Monthly operating cost

$35.94

≈ 7 cups of coffee

Total wattage1,152 W

Breaker size15 A

Recommended voltage120 V

Mat length48 lin ft

How to Use This Calculator

Enter the total room floor area in square feet.
Enter the percentage of floor area under cabinets and fixtures (not heated).
Set the heating output in watts per square foot (12 W is standard; 15–20 W for cold climates).
Enter average daily run time in hours and your local electricity rate in $/kWh.
Review the daily and monthly operating cost, mat roll dimensions needed, and circuit load.

How the result changes with Room area

Room area	Heated area	Thermostats needed	Monthly operating cost
509	407.2 sq ft	3	$152.46
1,757	1,405.6 sq ft	10	$526.26
3,254	2,603.2 sq ft	18	$974.64
4,501	3,600.8 sq ft	25	$1,348.14

Room area: Total room floor area.
Fixtures / cabinets: Percentage of floor under cabinets, tubs, and permanent fixtures (not heated).
Watts per sq ft: Heating output: 12 W/sqft standard, 15-20 for cold climates.
Daily run time: Average hours the heating runs per day.
Electricity rate: Your local electricity cost per kWh.
Mat width: Heating mat width: 1.5', 2', or 3' rolls.

Heated area: Floor area that will receive heating mats.
Total wattage: Total electrical load of the heating system.
Breaker size: Minimum circuit breaker (NEC 80% rule).
Recommended voltage: 120V for small areas (<150 sqft), 240V for larger.
Thermostats needed: Number of thermostat/relay zones (max 150 sq ft each).
Mat length: Total linear feet of heating mat at chosen width.
Monthly operating cost: Estimated monthly electricity cost to run the system.

Identify Input Parameters
4 parameters
Room area = 120, Fixtures / cabinets = 20, Watts per sq ft = 12, Daily run time = 8 = 6 input(s) provided
Calculate Heated area
Heated area = roomAreaSqFt * (1 - fixturePct / 100)
96 = 96
Calculate Thermostats needed
Thermostats needed
1 = 1
Calculate Monthly operating cost
Monthly operating cost = monthlyKwh * kwhRate
35.94 = $35.94
Calculate Total wattage
Total wattage = heatedAreaSqFt * wattsPerSqFt
1152 = 1152
Calculate Breaker size
Breaker size
15 = 15