Power Calculator
The Power Calculator computes electrical power from voltage and current. It is useful for sizing appliances, checking circuit loads, and understanding how much energy a device consumes.
Power Calculator
V
A
What the result means
Power is the rate at which electrical energy is converted into another form, such as heat, light, or motion. It is the product of voltage and current. The energy per hour figure tells you how much energy the device consumes if it runs continuously for one hour.
How to use this calculator
- 1Enter the voltage in volts (V).
- 2Enter the current in amperes (A).
- 3Press Calculate to see the power in watts (W) and the energy used per hour in watt-hours (Wh).
- 4Review the formula P = V × I shown with the result.
- 5Adjust the inputs to compare different devices or operating conditions.
The formula
The calculation uses a standard, verifiable formula. Here it is in its simplest form.
P = V × I
Where:
P = Power (W)
V = Voltage (V)
I = Current (A)
Energy per hour = P × 1 hour (Wh)
What each variable means
| Symbol | Name | Description |
|---|---|---|
| V | Voltage | The electrical potential difference, measured in volts. |
| I | Current | The flow of electric charge, measured in amperes. |
| P | Power | The rate of energy conversion, measured in watts. |
Step-by-step example
Example: 230 V and 5 A
Voltage:230 VCurrent:5 A
- 1Power = 230 × 5 = 1150 W
- 2Energy per hour = 1150 Wh = 1.15 kWh
- 3Running this device for 1 hour consumes 1.15 kWh.
Result
P = 1150 W (1.15 kWh per hour)
What changes the result
- Higher voltage or current increases power consumption.
- Power ratings on appliances indicate their maximum consumption.
- Energy cost depends on both power and how long the device runs.
Edge cases to be aware of
Unusual situations handled correctly
- If voltage or current is zero, power is zero.
- AC circuits with power factor less than 1 will have lower real power than V × I suggests.
- Very high power values may indicate a circuit overload risk.
Common mistakes
Avoid these errors
- Using peak values instead of RMS values for AC circuits.
- Forgetting the power factor in AC circuits.
- Confusing watts (power) with watt-hours (energy).
Assumptions
- The circuit is DC or purely resistive AC.
- Voltage and current are in phase (power factor = 1).
- The values are steady, not transient peaks.
Limitations
- Does not account for power factor in AC circuits.
- Assumes constant voltage and current.
- Real devices may draw different power at different times.
Frequently asked questions
What is the difference between watts and watt-hours?+
Watts measure power — the rate of energy use at a moment. Watt-hours measure energy — the total amount used over time. A 100 W bulb running for 2 hours uses 200 Wh of energy.
How do I calculate power in an AC circuit?+
For AC circuits, real power is P = V × I × power factor. The power factor accounts for the phase difference between voltage and current caused by inductive or capacitive loads.
Why does my appliance have a power rating?+
The power rating tells you the maximum rate at which the appliance converts electrical energy. It helps you size circuits, choose the right cable, and estimate running costs.