How to read the kWh on your electricity bill
The bill charges for energy, not power. Power (watts, W) says how fast an appliance uses electricity at a given moment; energy (kilowatt-hours, kWh) is what adds up over time. One kWh is what a 1000 W appliance uses in one hour, or a 100 W one in ten hours.
Your daily use
Find the kWh for the billing period and the number of days on the bill, and divide. If the bill shows 186 kWh over 31 days, you use 6 kWh a day. That number lets you compare months and, later on, size a solar system.
What one appliance uses
The formula is: power (W) × hours of use per day ÷ 1000 = kWh per day. The power is on the appliance’s label or in the manual.
Example. A fridge with a 150 W compressor does not run all day: it starts and stops. If the compressor runs about 10 hours a day in total, 150 × 10 ÷ 1000 = 1.5 kWh a day, about 45 kWh a month. At USD 0.20 per kWh, that is about USD 9 a month.
| Appliance | Typical power | Daily use | kWh/day |
|---|---|---|---|
| LED bulb | 9 W | 5 h | 0.05 |
| Television | 80 W | 4 h | 0.32 |
| Fan | 50 W | 8 h | 0.40 |
| Iron | 1200 W | 15 min | 0.30 |
| Electric shower | 4500 W | 20 min | 1.50 |
Standby use
Chargers, set-top boxes and anything with a standby light use power even when you are not using them. Each one usually draws 1 to 5 W; ten devices at 3 W add up to 0.72 kWh a day, over 20 kWh a month. A power strip with a switch fixes it.
Measuring it properly
The label gives maximum power, not average. A cheap plug-in meter shows the real kWh after a day or a week of use, and it is the most reliable way to find out which appliance costs the most.