How Electricity Is Billed
Electricity is sold by the kilowatt hour — one kilowatt of power drawn for one hour. A 1,000 W appliance running for one hour uses exactly 1 kWh; a 100 W bulb needs ten hours to use the same.
kWh = Watts ÷ 1,000 × Hours
Cost = kWh × Rate per kWh
Note the distinction between power and energy. Watts measure the rate of use at an instant; kilowatt hours measure the quantity consumed over time. Your meter records the second.
Typical Appliance Power
| Appliance | Watts | kWh per hour | Cost per hour at $0.17 |
|---|---|---|---|
| LED bulb | 10 | 0.01 | $0.002 |
| Laptop | 50 | 0.05 | $0.009 |
| Television | 120 | 0.12 | $0.020 |
| Refrigerator (cycling average) | 150 | 0.15 | $0.026 |
| Desktop computer | 200 | 0.20 | $0.034 |
| Washing machine | 500 | 0.50 | $0.085 |
| Microwave | 1,000 | 1.00 | $0.170 |
| Space heater | 1,500 | 1.50 | $0.255 |
| Electric kettle | 1,500 | 1.50 | $0.255 |
| Dishwasher | 1,800 | 1.80 | $0.306 |
| Tumble dryer | 3,000 | 3.00 | $0.510 |
| Central air conditioning | 3,500 | 3.50 | $0.595 |
The pattern worth internalising: anything that makes heat or moves it — heating, cooling, drying, cooking, hot water — dominates a household bill. Electronics and lighting are rounding errors by comparison.
Where the Money Actually Goes
| Category | Share of a typical U.S. bill |
|---|---|
| Heating and cooling | ~45% |
| Water heating | ~14% |
| Appliances (fridge, laundry, dishwasher) | ~13% |
| Lighting | ~9% |
| Electronics | ~7% |
| Everything else | ~12% |
Replacing every bulb in a house with LEDs is worth real money, but adjusting the thermostat by two degrees usually saves more.
Standby Power
Devices that appear off still draw power — "vampire" or standby load. Individually trivial, collectively it accounts for roughly 5–10% of household electricity.
| Device on standby | Watts | Cost per year at $0.17 |
|---|---|---|
| Television | 1–3 | $1.50–$4.50 |
| Games console (rest mode) | 10–15 | $15–$22 |
| Cable or satellite box | 15–30 | $22–$45 |
| Desktop PC (sleep) | 3–5 | $4.50–$7.50 |
| Phone charger, nothing plugged in | 0.1–0.5 | $0.15–$0.75 |
The set-top box is usually the worst offender in a home, because it often draws nearly as much off as on.
Understanding Your Tariff
- Flat rate — one price per kWh at any hour. Simplest to calculate.
- Time of use — higher during peak hours, cheaper overnight. Shifting laundry and dishwashing to off-peak can cut those loads by half.
- Tiered — the price per kWh rises after a monthly threshold, so the last units cost far more than the first.
- Standing charge — a fixed daily fee regardless of use, which this calculator does not include.
Your effective rate is the total bill divided by the kWh used, and that is the figure to enter here — it captures taxes, delivery charges and the standing charge spread across your consumption.
Reducing the Bill
- Heating and cooling first. One degree on the thermostat is worth roughly 1–3% of heating cost.
- Wash cold. About 90% of a washing machine's energy heats the water.
- Air-dry laundry. The tumble dryer is usually the single most expensive appliance in a home.
- Switch to LED. An LED uses about a tenth of an incandescent bulb for the same light.
- Use a smart plug to measure. Nameplate ratings are maximums, not averages; a fridge rated 150 W cycles on and off and may average 40.
Frequently Asked Questions
How do I find an appliance's wattage?
Check the label on the back or underneath, or the manual. If only volts and amps are given, multiply them — the calculator does this for you in the volts-and-amps mode.
Why is my bill higher than this calculation?
Because this covers one appliance. Add the standing charge, taxes and delivery fees, and remember that nameplate wattage is the maximum draw rather than the average.
What is a typical rate per kWh?
The U.S. average is around $0.17, ranging from about $0.11 in some states to over $0.40 in Hawaii and California. UK and EU rates commonly sit between £0.24 and €0.35.
Does a device use more electricity when it starts?
Motors and compressors draw a large surge for a fraction of a second, but it is far too brief to affect the bill. Leaving a fridge or air conditioner alone is better than switching it on and off.