What is a kilowatt-hour? It’s the unit your utility bills you in, and the unit home batteries are rated in. One kilowatt-hour (kWh) is 1,000 watts used for one hour, or 100 watts for 10 hours. Once you understand it, you can estimate what any appliance costs and how big a battery or solar system you need.
What Is a Kilowatt-Hour? Power vs Energy
- Watts (W) measure power, a rate, like speed.
- Watt-hours (Wh) and kilowatt-hours (kWh) measure energy, an amount, like distance.
Example math: a 1,500W space heater running 2 hours = 1.5 kW × 2 h = 3 kWh.
kWh on Your Electric Bill
Your bill shows:
- Total kWh used this billing period (meter reading difference)
- Price per kWh, sometimes split into tiers or time-of-use periods
- Fixed charges that don’t depend on kWh
The US average household uses roughly 860 kWh a month (EIA), about 29 kWh a day. Your number may differ a lot with climate, home size, and electric heat or EVs.
Estimating What an Appliance Costs
Cost = watts × hours ÷ 1,000 × price per kWh
Example math at $0.17/kWh (illustrative; use your own rate):
| Appliance | Use | kWh | Cost |
|---|---|---|---|
| 60W TV | 5 h/day | 0.3/day | ~$1.50/month |
| Fridge | 450 kWh/yr | 1.2/day | ~$6.40/month |
| 1,500W space heater | 4 h/day | 6/day | ~$31/month |
| EV, 30 mi/day at 0.3 kWh/mi | Daily | 9/day | ~$46/month |
kWh for Batteries and Solar
- Battery capacity is in kWh: a 13.5 kWh battery can deliver about 13.5 kW for one hour, or 1 kW for 13.5 hours (minus losses).
- Solar production is in kWh: a 6 kW array might make roughly 20–30 kWh on a good day, depending on location.
- Portable power stations use Wh: 3,600Wh = 3.6 kWh.
Reading Time-of-Use Rates
On a time-of-use plan, the same kWh costs more in the evening peak (often around 4–9 p.m.) than overnight. Moving flexible loads, such as laundry, dishwashers and EV charging, to cheaper hours cuts the bill without using fewer kWh. Home batteries do the same thing automatically.
kW vs kWh
A kW rating tells you how much can run at once. A kWh rating tells you how long. You need both when you shop for a battery.
Worked Example: What Does Each Appliance Cost a Month?
Illustrative usage at the EIA’s 2024 U.S. average residential price of about 16.5¢ per kWh:
| Appliance | Watts | Hours a day | kWh a month (30 days) | Cost a month |
|---|---|---|---|---|
| LED bulb | 10W | 5 | 1.5 | about $0.25 |
| 55 in. LED TV | 100W | 4 | 12 | about $1.98 |
| Space heater | 1,500W | 4 | 180 | about $29.70 |
| Window AC | 900W | 8 | 216 | about $35.64 |
| Refrigerator (EnergyGuide 600kWh/ | n/ | n/ | 50 | about $8.25 |
Formula: watts × hours ÷ 1,000 = kWh, then kWh × rate. Rates vary widely by state; your bill shows your actual rate. See how to read an appliance label.
Key Numbers
| Number | Value | Source |
|---|---|---|
| Average U.S. home use, 2023 | about 10,500kWh a year (about 875kWh a month) | EIA |
| Average residential price, 2024 | about 16.5¢ per kWh | EIA |
| Tesla Powerwall 3 usable capacity | 13.5kWh | Tesla datasheet |
| 12.8V 100Ah LiFePO4 battery | 1.28kWh | Calculated |
kWh for Solar Sizing
Solar production is also measured in kWh. NREL’s PVWatts calculator estimates yearly kWh for a system at your address. Illustrative math: if PVWatts shows 1,350kWh per kW of panels a year and you use 10,500kWh, you need about 7.8kW of panels. See how many solar panels do I need and read your electric bill before solar.
kWh for Battery Backup
To estimate backup time, divide usable battery kWh by your hourly use during an outage. Illustrative: 13.5kWh ÷ 1.2kW of essential loads ≈ 11 hours. More in how many batteries to power a house.
Other Units You’ll See
- Wh: 1/1,000 of a kWh; used on small batteries and power stations.
- MWh: 1,000kWh; used for utility-scale projects.
- Therm: a natural gas unit, about 29.3kWh of heat energy.
FAQ
How much is 1 kWh?
Whatever your utility charges. US residential averages have been in the mid-to-high teens of cents per kWh recently, varying a lot by state.
How many kWh does a house use per day?
About 29 kWh on average in the US. Check your bill.
Is a kWh the same as a kW?
No. kW is power (rate). kWh is energy (amount).
How do I find my rate per kWh?
Divide your bill’s energy charges by kWh used, or look for the per-kWh rate printed on the bill.
Why does my bill have charges that aren’t per kWh?
Many utilities add fixed monthly customer charges and, for some plans, demand charges in kW.
Sources: U.S. Department of Energy, “Estimating Appliance and Home Electronic Energy Use” and “How Does Electricity Work?”; EIA residential electricity FAQ; ENERGY STAR; EIA Electric Power Monthly and residential use FAQ; NREL PVWatts. Accessed Oct 2026.
Related: EcoFlow Delta 3 Max Price per Wh, Jackery HomePower 3600 Plus: What Can It Power?