Underfloor Heating Calculator
Cable/mat length and running cost for radiant floor heat.
Enter your values
Enter the heated area in sq ft.
Enter the heating density in W/sq ft.
Enter the hours per day in hr.
Enter the electricity rate in $/kWh.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- System power
- 960 W
- Daily energy use
- 3.84 kWh
- Estimated daily cost
- $0.61
- Estimated monthly cost
- $18.43
Quick answer
Underfloor heating cable length depends on room area and spacing, and running cost depends on wattage, hours of use and electricity rate.
power = area x W/sq ft; cost = power(kW) x hours x rate
At a glance
| What it does | Cable/mat length and running cost for radiant floor heat. |
|---|---|
| Category | Home & DIY |
| Inputs needed | Heated area, Heating density, Hours per day, Electricity rate |
| Main output | System power |
| Formula | power = area x W/sq ft; cost = power(kW) x hours x rate |
| Cost | Free — no sign-up, no download |
How to use the Underfloor Heating Calculator
- 1Measure the floor area to be heated (not the whole room if under cabinets are excluded).
- 2Use 10-15 W/sq ft for supplemental heat in most climates.
- 3Estimate daily run hours and your electricity rate to see running cost.
Inputs explained
- Heated area(sq ft)
- Enter the heated area in sq ft.
- Heating density(W/sq ft)
- Enter the heating density in W/sq ft.
- Hours per day(hr)
- Enter the hours per day in hr.
- Electricity rate($/kWh)
- Enter the electricity rate in $/kWh.
Worked example
Using the values the calculator loads with:
Inputs
- Heated area80 sq ft
- Heating density12 W/sq ft
- Hours per day4 hr
- Electricity rate0.16 $/kWh
Results
- System power960 W
- Daily energy use3.84 kWh
- Estimated daily cost$0.61
- Estimated monthly cost$18.43
Frequently asked questions
Can underfloor heating be a primary heat source?
In well-insulated homes yes, but most systems are installed as supplemental comfort heat.
Electric or hydronic?
Electric is easier to retrofit into a single room; hydronic is more efficient for whole-house systems.
What do I need to enter into the Underfloor Heating Calculator?
Just 4 values: heated area, heating density, hours per day, electricity rate. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Underfloor Heating Calculator work out the answer?
Underfloor heating cable length depends on room area and spacing, and running cost depends on wattage, hours of use and electricity rate. It applies the formula power = area x W/sq ft; cost = power(kW) x hours x rate and shows the working so you can check each step by hand.
Is the Underfloor Heating Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.