How to Calculate Electrical Power and Energy Cost
Electrical power is the rate at which an appliance consumes energy. Understanding how to calculate power consumption helps you estimate electricity bills, identify energy-hungry appliances, and make informed decisions about energy efficiency. Power in watts times time in hours gives energy in watt-hours (Wh) or kilowatt-hours (kWh) — the unit used on electricity bills.
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Formula
Electric Power Calculator
Calculate electrical power, energy consumption, and running cost.
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Worked Example
Given:
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FAQs
How do I find the wattage of an appliance?
Most appliances have a label (usually on the back or bottom) showing rated power in watts or VA (volt-amperes). Alternatively, calculate from current and voltage: P = V × I. Smart plugs with energy monitoring can measure actual consumption, which may differ from rated power.
What is the difference between kW and kWh?
Kilowatt (kW) is a unit of power — rate of energy consumption at a moment in time. Kilowatt-hour (kWh) is a unit of energy — the total energy consumed over time. A 1 kW appliance running for 1 hour uses 1 kWh. Electricity bills charge for kWh consumed.
How do I reduce my electricity bill?
Identify high-wattage appliances used frequently — electric heating, hot water, air conditioning, and tumble dryers are the biggest consumers. Replace with efficient alternatives (heat pumps, LED lights), reduce usage time, and shift consumption to off-peak hours if your utility offers time-of-use pricing.