Home / Life skills / Watts and kWh
Skills · Home
Watts, kWh and Your Electricity Bill
Why does the space heater cost so much more than the TV? Learn the three numbers on every plug and bill, and work out exactly what each appliance costs you.
~10 min4 lessonsAppliance cost calculator5-question quiz
01
Volts, amps and watts
Think of electricity like water in a pipe:
- Volts (V) are the pressure. Homes are about 120 V in North America and 230 V in most other places.
- Amps (A) are the flow: how much current moves.
- Watts (W) are the power: how fast energy is used. It's the number that matters for your bill.
watts = volts × ampsa 10 A heater on 120 V uses 1,200 W
02
Kilowatt-hours: what you pay for
Your bill charges for energy: power multiplied by time. The unit is the kilowatt-hour (kWh): 1,000 watts running for one hour.
kWh = watts × hours ÷ 1,000
Example · a 1,500 W heater for 4 hours
- 1,500 × 4 ÷ 1,000 = 6 kWh
- At $0.17 per kWh: 6 × 0.17
- ≈ $1.02 a day, around $30 a month
Example · a 10 W LED bulb for 5 hours a day
- 10 × 5 ÷ 1,000 = 0.05 kWh a day
- × 30 days = 1.5 kWh
- ≈ 26¢ a month
03
What uses the most
| Appliance | Typical power |
|---|---|
| Space heater | 1,500 W |
| Electric oven | 2,000–5,000 W |
| Clothes dryer | 2,000–5,000 W |
| Kettle | 1,500–3,000 W (but only for minutes) |
| Fridge | 100–200 W (cycling on and off) |
| TV | 50–150 W |
| Laptop | 30–70 W |
| LED bulb | 8–12 W |
Anything that heats or cools uses the most. A kettle is very powerful but runs so briefly it costs little; a heater on all evening adds up fast.
The watts are on a sticker or plate on the back or bottom of most appliances.
04
Reading your bill
- Usage in kWh for the billing period, sometimes compared with last year.
- Rate per kWh. It may change by time of day (“time-of-use”), so running the dishwasher at night can be cheaper.
- Fixed or standing charge: a daily or monthly fee you pay regardless of usage.
To find your real rate, divide the energy part of the bill by the kWh used.
Try it · appliance cost calculator