What Is Kilowatt second?
A kilowatt second is a unit for measuring energy. It tells you how much energy is used when something with a power of one kilowatt runs for one second.
This unit combines two ideas you may already know. Power in kilowatts and time in seconds. When you multiply them, you get energy in kilowatt seconds.
Definition
One kilowatt second is the amount of energy used by a device that uses one kilowatt of power for one second.
- 1 kilowatt kW is 1000 watts W.
- 1 second s is the basic unit of time.
- 1 kilowatt second kW·s is equal to 1000 joules J of energy.
- This also means 1 kilowatt second is exactly the same amount of energy as 1 kilojoule kJ.
So in simple words, kilowatt second and kilojoule are two names for the same size of energy.
History / Origin
The kilowatt second comes from the International System of Units SI. In SI, the basic unit of energy is the joule J. A watt is defined as one joule per second.
Because 1 watt is 1 joule each second, multiplying kilowatts by seconds naturally gives joules. Over time, scientists and engineers started to use short forms like watt second W·s and kilowatt second kW·s to talk about energy in a clear way, especially when working with electric power.
Today, the joule and the kilojoule are more common in science. The kilowatt hour kWh is more common on electricity bills. The kilowatt second is still correct and useful but is seen less often.
Symbol & Abbreviation
The main ways to write kilowatt second are:
- Name kilowatt second
- Official symbol kW·s
- Other common forms kWs or kW s
All of these mean the same unit. The form kW·s is the clearest, because the dot shows that kilowatts are multiplied by seconds.
Current Use Around the World
Globally, the kilowatt second is a correct SI based unit, but it is not the most popular way to show energy.
In practice:
- Scientists and engineers usually use joules J or kilojoules kJ.
- Power companies and home energy bills almost always use kilowatt hours kWh.
- Some technical papers and calculations for electric power may briefly use kilowatt seconds, mainly as a step to get values in joules or kilojoules.
Even though it is not very common, knowing the kilowatt second helps you see the link between power kilowatts, time seconds, and energy joules.
Example Conversions
Here are some clear examples to show how kilowatt seconds relate to other energy units.
To joules J and kilojoules kJ
- 1 kW·s = 1000 J
- 1 kW·s = 1 kJ because 1 kJ = 1000 J
- 5 kW·s = 5000 J = 5 kJ
- 0.5 kW·s = 500 J = 0.5 kJ
To watt seconds W·s
- 1 kW·s = 1000 W·s since 1 kW = 1000 W
- 10 kW·s = 10,000 W·s
To kilowatt hours kWh
There are 3600 seconds in one hour. So:
- 1 kWh = 1 kW × 1 h = 1 kW × 3600 s = 3600 kW·s
- Therefore 1 kW·s = 1 ÷ 3600 kWh ≈ 0.0002778 kWh
Some worked examples:
- 500 kW·s = 500 ÷ 3600 kWh ≈ 0.139 kWh
- 3600 kW·s = 3600 ÷ 3600 kWh = 1 kWh
- 100 kW·s ≈ 0.0278 kWh
Everyday style example
Imagine an electric heater that uses 2 kW of power and runs for 10 seconds.
- Energy in kW·s = 2 kW × 10 s = 20 kW·s
- In joules this is 20 × 1000 J = 20,000 J
- In kWh this is 20 ÷ 3600 ≈ 0.0056 kWh
Related Units
The kilowatt second is closely linked to these other energy and power units:
- Watt second W·s a smaller unit of energy. 1 kW·s = 1000 W·s.
- Joule J the basic SI unit of energy. 1 kW·s = 1000 J.
- Kilojoule kJ 1000 joules. 1 kW·s = 1 kJ exactly.
- Kilowatt hour kWh widely used on electricity bills. 1 kWh = 3600 kW·s.
- Megajoule MJ 1,000,000 joules. 1 MJ = 1000 kW·s.
FAQs
- Is kilowatt second a unit of power or energy?
It is a unit of energy. Power kilowatt tells how fast energy is used. Time second tells how long. Together they give total energy used. - How is kilowatt second different from kilowatt hour?
Both measure energy, but they use different times. Kilowatt second uses seconds. Kilowatt hour uses hours. There are 3600 kilowatt seconds in one kilowatt hour. - Is 1 kilowatt second the same as 1 kilojoule?
Yes. 1 kW·s equals 1000 joules. 1 kJ also equals 1000 joules. So 1 kW·s and 1 kJ represent the same amount of energy. - Why do electricity bills use kWh and not kW·s?
Homes and businesses care about energy used over many hours, not just seconds. Using kilowatt hours gives smaller, easier numbers for daily and monthly use. - When might someone use kilowatt seconds?
Engineers or scientists might use kilowatt seconds when working with short time periods, fast electrical events, or when they want a neat link between power in kW and energy in kJ. - How do I convert from kW·s to kWh?
Divide the value in kW·s by 3600. For example, 7200 kW·s ÷ 3600 = 2 kWh. - How do I convert from kW·s to joules?
Multiply the value in kW·s by 1000. For example, 3 kW·s = 3 × 1000 J = 3000 J.
