Power Calculator
Calculate electrical power
Frequently Asked Questions
How does the Power Calculator work?
Enter any two of voltage, current, resistance, or power, and the calculator computes the remaining values using Ohm's Law and the power formula. For example, enter 120V and 2A to get 240W power and 60Ω resistance.
What is electrical power measured in?
Power is measured in watts (W). 1 watt = 1 volt × 1 ampere. Common multiples: kilowatt (kW = 1,000W), megawatt (MW = 1,000,000W). A typical household uses 1-2 kW average, with peaks of 5-10 kW.
How do I calculate electricity cost from power consumption?
Cost = Power (kW) × Time (hours) × Rate ($/kWh). A 100W light bulb running 10 hours at $0.12/kWh costs: 0.1 × 10 × 0.12 = $0.12. The calculator can estimate daily, monthly, and annual electricity costs.
What is the difference between watts and watt-hours?
Watts measure instantaneous power (rate of energy use). Watt-hours measure total energy consumed over time. A 60W bulb running for 5 hours uses 300 Wh (0.3 kWh). Your electricity bill is based on kWh consumed.
How do I size a generator or UPS?
Add up the wattage of all devices you need to power simultaneously. Include a 20-25% safety margin. For example: computer 300W + monitor 50W + router 15W = 365W. With margin: 365 × 1.25 = 456W minimum capacity.