Electrical Power Formula
Calculate electrical power using P = VI, P = I²R, and P = V²/R.
Essential for circuit design, energy consumption, and component sizing.
The Formula
Electrical power measures the rate at which electrical energy is consumed or produced.
All three forms are equivalent — use whichever matches the values you know.
Variables
| Symbol | Meaning |
|---|---|
| P | Power (Watts, W) |
| V | Voltage (Volts, V) |
| I | Current (Amperes, A) |
| R | Resistance (Ohms, Ω) |
Which Form to Use
- P = V × I — when you know voltage and current
- P = I²R — when you know current and resistance
- P = V² / R — when you know voltage and resistance
Example 1
A 230 V appliance draws 4 A of current. What is its power consumption?
P = V × I
P = 230 V × 4 A
P = 920 W
Example 2
A 100 Ω resistor has 2 A flowing through it. How much power does it dissipate?
P = I²R
P = (2)² × 100
P = 4 × 100
P = 400 W
When to Use It
Use the electrical power formula when you need to:
- Calculate energy consumption of appliances and devices
- Size fuses, circuit breakers, and wiring
- Determine heat dissipation in resistors and components
- Calculate electricity costs (Power × Time = Energy in kWh)
For AC circuits, the formula becomes P = V × I × cos(φ), where cos(φ) is the power factor.
The power factor accounts for the phase difference between voltage and current in reactive circuits.