Power Calculator

Last updated: June 2026

Mode

Energy

kWh

Energy unit

Time

hours

Time unit

Power

2,000 W

2 kW

kWh

7.2 kWh

2.682 hp

Formula

Power = energy / time. Energy = power x time. Time = energy / power. 1kWh = 3,600,000J and 1hp = 745.7W.

Power references

Appliance	Typical power
Kettle	2-3 kW
Microwave	0.8-1.2 kW
Electric oven	2-3 kW
EV charger	7 kW

About this calculator

The Power Calculator works out power, energy, or time using the relationship between work done and time taken. It is useful for science lessons, electrical appliance checks, machinery examples, energy use estimates, and converting between watts, kilowatts, horsepower, joules, and kilowatt-hours.

Power, energy, and time formulas

Power is the rate of energy transfer. A higher power device uses or transfers the same amount of energy in less time.

power = energy / time
energy = power x time
time = energy / power
1 kWh = 3,600,000 J
1 hp = 745.7 W

How to use the power calculator

Choose whether to calculate power, energy, or time.
Enter the two known values.
Select units for power, energy, and time.
Use watts for physics examples and kilowatts for appliances.
Use kWh when comparing electricity use and bills.
Review equivalent units such as W, kW, and hp.

Worked examples

Kettle energy use

Input: 3 kW kettle running for 5 minutes

Calculation: energy = 3 kW x 5/60 hours

Result: 0.25 kWh

Mechanical power

Input: 10,000 J transferred in 20 seconds

Calculation: power = 10,000 / 20

Result: 500 W

Power vs energy

Power is a rate. Energy is the total amount transferred. A 2 kW appliance running for one hour uses 2 kWh of energy.

Everyday power references

Item	Typical power
Kettle	2-3 kW
Microwave	0.8-1.2 kW
EV home charger	Around 7 kW
LED bulb	5-12 W

Power estimate limitations

Real devices may vary by operating mode, efficiency, voltage, duty cycle, and manufacturer rating. Use measured data for billing or engineering decisions.

Frequently asked questions

What is power measured in?

Power is measured in watts.

What is a kilowatt-hour?

A kilowatt-hour is energy: one kilowatt of power used for one hour.

Is horsepower a power unit?

Yes. One mechanical horsepower is about 745.7 watts.

How do I calculate appliance energy use?

Multiply power in kilowatts by running time in hours to get kWh.

Does power always mean electricity?

No. Power can describe any rate of energy transfer, including mechanical work.

Related calculators

Kinetic Energy Calculator
Electricity Cost Calculator
Energy Bill Calculator

What does this mean?

This calculator is designed to help you understand the likely number before you make a decision or start an application.

Your result should be checked against official UK guidance, especially if your circumstances include dependants, exemptions, prior leave, or a complex immigration history.

Treat the figure as a planning tool rather than legal advice. Where the answer affects an application deadline or major payment, speak to an authorised adviser.