Power Calculator – Electrical Power, Voltage, Current, Resistance
Calculate electrical power from voltage, current, and resistance
How to Use
- Enter any two values: voltage (V), current (I), resistance (R), or power (P)
- Leave the values you want to calculate empty
- Click calculate to see all calculated values
- The calculator uses power formulas: P = V × I, P = V² / R, P = I² × R
What is Electrical Power?
Electrical power is the rate at which electrical energy is transferred by an electric circuit. It represents how much work is done by electricity per unit of time and is measured in watts (W).
Power is a fundamental concept in electrical engineering and is critical for designing circuits, selecting components, and ensuring electrical safety.
Power Formulas
Electrical power can be calculated using different formulas depending on which variables you know:
- P = V × I (Power equals voltage times current)
- P = V² / R (Power equals voltage squared divided by resistance)
- P = I² × R (Power equals current squared times resistance)
These formulas are derived from Ohm's law (V = I × R) and the basic power formula.
Units
Standard electrical units:
- Voltage (V): measured in Volts
- Current (I): measured in Amperes (Amps)
- Resistance (R): measured in Ohms (Ω)
- Power (P): measured in Watts (W)
Larger units include kilowatts (kW = 1,000 W) and megawatts (MW = 1,000,000 W).
Applications
Power calculations are essential in:
- Electrical circuit design and analysis
- Power supply and battery selection
- Motor and appliance specifications
- Heating element design
- Energy consumption calculations
- Electrical safety and fuse/breaker sizing
- Solar panel and renewable energy systems
- LED and lighting design
Power Dissipation
When current flows through a resistor, electrical energy is converted to heat. This is called power dissipation and must be considered when selecting components to prevent overheating and damage.
Resistors, transistors, and other components have power ratings that should not be exceeded. Always ensure the calculated power is less than the component's rated power with an appropriate safety margin.
Frequently Asked Questions
- What is the difference between power and energy?
- Power is the rate at which energy is transferred or used (measured in watts), while energy is the total amount of work done (measured in joules or watt-hours). Energy = Power × Time.
- How do I calculate power if I only know voltage and resistance?
- Use the formula P = V² / R. Square the voltage and divide by the resistance to get power in watts.
- Why does the power calculator show four formulas?
- The calculator uses three main power formulas (P = V × I, P = V² / R, P = I² × R) plus Ohm's law (V = I × R) to calculate all four values from any two inputs.
- What happens if a component exceeds its power rating?
- Exceeding the power rating can cause overheating, component damage, or failure. Always select components with power ratings higher than the calculated power, typically with a 25-50% safety margin.