Key takeaways
- Power is P = V × I: voltage times current, measured in watts.
- Power is a rate — it measures how fast energy is used, not how much total energy is used.
- A kettle rated at 1,500 W uses energy far faster than a 5 W LED bulb.
- Watts combine both voltage and current — neither one alone tells you the power.
In this guide
What is electrical power?
Power is the rate at which electrical energy is used or delivered. A device with higher power uses energy faster, which is why high-power appliances like kettles heat up quickly.
Why does electrical power matter?
Power ratings decide how much a device costs to run and what size fuse or wire it needs. A device pulling more watts draws more current for the same voltage, which matters for safety.
A 1,500 W kettle and a 5 W LED bulb can both plug into the same wall socket, but the kettle draws roughly 300 times more current, and uses energy 300 times faster.
The formula
| Symbol | What it means | Example |
|---|---|---|
| P | The power, in watts (W) | 24 W |
| V | The voltage, in volts (V) | 12 V |
| I | The current, in amps (A) | 2 A |
How to calculate power step by step
- 1Find the voltage. Note the voltage supplied to the device, in volts.
- 2Find the current. Note the current the device draws, in amps.
- 3Multiply voltage by current.
V × Igives you the power. - 4Write the answer in watts. That's the rate of energy use.
Try the calculator below with your own voltage and current to see the steps laid out.
Try it yourself
Pre-filled with the example — change any value.
Common mistakes to avoid
- Mixing up power and energy. Power (watts) is a rate; energy, like the kilowatt-hours on an electricity bill, is power used over time.
- Using the wrong current. Always use the device's actual operating current, which you can find with Ohm's Law if you know voltage and resistance.
- Forgetting units. Keep voltage in volts and current in amps, or the answer won't be in watts.
Tips and tricks
- To estimate an appliance's running cost, multiply its watts by the hours used, then divide by 1,000 to get kilowatt-hours.
- A quick sanity check: household devices under about 100 W are usually electronics, and anything over 1,000 W is usually a heater or kettle.
- Power and work done share the same idea — one measures the rate, the other the total amount of energy.
Where you'll use it in real life
- Appliances: power ratings on a kettle, hairdryer, or heater tell you how much electricity they draw.
- Home safety: knowing a device's power helps choose the right fuse or circuit breaker.
- Bills: your electricity bill is really total power used over time, added up across every device in the house.
- Electronics: engineers use the power formula to size batteries and chargers correctly.
Quick summary
To find electrical power, multiply voltage in volts by current in amps. The result is in watts, and higher watts always mean energy is being used faster. Use the calculator above to check your own device's power rating.
Worked example
A small kitchen appliance runs on 12 volts and draws 2 amps of current. What is its power rating in watts?
- 01P = V × I
- 02P = 12 × 2
- 03P = 24 W
These numbers are pre-filled in the calculator above.
Frequently asked questions
How do I calculate power from voltage and current?
Multiply the voltage in volts by the current in amps: P = V × I. The result is in watts.
What is the difference between power and energy?
Power is how fast energy is used, measured in watts. Energy is the total amount used over time, often measured in kilowatt-hours.
Why do some appliances draw more current than others?
For the same voltage, a higher-power appliance needs more current, since power equals voltage multiplied by current.
What is a watt in everyday terms?
A watt is a small unit of power. A typical LED bulb uses around 5 to 10 watts, while a kettle uses over 1,000 watts.
