Electricity Usage Calculator
Calculate daily and monthly electricity use from appliance wattage and run time.
How Electricity Usage Is Calculated
Electricity consumption is commonly measured in kilowatt-hours (kWh). The calculator converts appliance power from watts to kilowatts and multiplies it by the number of hours the appliance operates each day.
Formula
Daily Energy (kWh) = Power (W) × Hours per Day ÷ 1,000
Worked Example
A 1,500-watt heater used for 4 hours per day consumes 1,500 × 4 ÷ 1,000 = 6 kWh per day. Over 30 days, that is approximately 180 kWh.
Factors That Affect Actual Usage
Rated wattage may differ from real operating power. Thermostats, variable-speed motors, standby modes, duty cycles and energy-saving settings can reduce or vary consumption. For appliances that cycle on and off, use average operating hours rather than total time plugged in.
Frequently Asked Questions
What is a kilowatt-hour?
A kilowatt-hour is the energy used by a 1,000-watt device running for one hour.
Does an appliance always use its rated wattage?
No. Many appliances cycle or change power depending on load, temperature and operating mode.
How do I estimate electricity cost from this result?
Multiply the calculated kWh by your electricity rate per kWh, or use the related kWh Cost Calculator.
Methodology and Practical Limits
Electrical energy in kilowatt-hours equals power in kilowatts multiplied by operating hours. Devices that cycle or vary power need an average duty factor or measured consumption; standby use can also contribute to monthly energy.