Calculate electricity usage in kWh
Where P = watts, t = hours
| Appliance | kWh/day |
|---|---|
| Refrigerator | 1-2 |
| AC (window) | 3-5 |
| TV (4 hrs) | 0.4 |
| Washing machine | 0.5 |
Energy consumption is measured in kilowatt-hours (kWh). It represents the total amount of electricity used over time, as opposed to power (watts) which is the instantaneous rate of electricity use.
Energy (kWh) = Power (W) × Time (hours) ÷ 1000. A 100W bulb running for 10 hours uses 1 kWh.
Electric meters display cumulative kWh. To find usage for a period, subtract the previous reading from the current reading.
Energy (kWh) = Power (watts) × Time (hours) ÷ 1000. A 1500W heater running for 4 hours uses: 1500 × 4 ÷ 1000 = 6 kWh.
A kWh is a unit of energy (not power). It represents using 1000 watts for one hour, or any equivalent like 500 watts for 2 hours. Your electricity bill charges per kWh consumed.
US average is about 900 kWh/month (30 kWh/day). This varies greatly - from 500 kWh in apartments to 1500+ kWh in large homes with electric heating.
Typical breakdown: HVAC 40-50%, water heating 15%, appliances 15%, lighting 10%, electronics 10%. In hot climates, AC alone can be 50%+ of consumption.
kW (kilowatt) is power - the rate of energy use at any instant. kWh (kilowatt-hour) is energy - the total amount used over time. Think of kW as speed and kWh as distance traveled.
Use LED bulbs (75% less), set thermostat 2° higher/lower, unplug idle electronics, run full loads only, use cold water washing, and consider Energy Star appliances.