# kW to kWh Conversion

Will appreciate if someone enlighten me. I tried searching online but I am still confused.

Considering I have an hour of power - 25380 kW. How do I convert it to kWh (energy)?

I am not sure if I should use kWh = 25380 * 1hr or kWh = 25380 * 24hr

Thanks!

• How long do you plan to operate the device? – Turbo J May 1 '18 at 9:43
• "Considering I have an hour of power" – wrong. That's either power already or one hour (or any other arbitrary time) of energy. – Janka May 1 '18 at 9:59
• You might find The factor-label method for converting units useful for understanding how units of measurement combine. – Andrew Morton May 1 '18 at 11:02
• @Janka What's wrong with "an hour of power"? If I own a coin-activated generator I could sell you an hour of 25 kW. – pipe May 1 '18 at 19:17

Suppose someone asked you: I'm driving at 60 miles per hour, how far have I gone? Obviously, there's not enough information; you have to know how long they've been driving at that speed. If it's a minute, they've gone one mile; if it's an hour, they've gone 60 miles.

Same think with kW and kWh: the first is the rate that you're using energy (this is called power), and the second is the amount of energy that you've used. The fact that the names are so similar can be confusing.

One Watt is one Joule of energy every second.

So a 1000 Watt generator generates 1000 Joules of electrical energy every second.

A 100 Watt light bulb consumes 100 Joules of energy every second.

An ideal Battery that stores 3600 Joules of energy could release that at a rate of one Joule per second (1 Watt) for 3600 seconds (1 hour) - that is 1 Watt-hour. Or at ten Joules per second (10 watts) for 360 seconds (6 minutes) - that is also 1 Watt-hour.

It may help if you consider Watts conceptually equivalent to Litres per second from a tap/faucet/well/spring/stream and Watt-Hours equivalent to litres in a water-tank/lake.

Watt hours are really a rather odd unit of energy measurement that happens to be convenient for power companies dealing with customers whose education didn't really give them a solid grasp of SI units of energy (99% of people)

• I think it is probably because dealing in units of hours is more convenient then seconds when it comes to household energy use - even for those of us who understand SI units. It's much more useful to know how much my heater will cost to run per hour rather than per second, and a 3600 scale factor is not so easy to use when doing mental arithmetic. – Jon May 1 '18 at 11:46

If a light bulb of 60 Watts is on for 1 hour its total consumption is 60Wh. The SI is Ws (Wattseconds), if something is consuming 5W and is powered for 2 Minutes its total power consumption was 600Ws. So it's $E = P*t = 25380kW * 1hr = 25'380kWh$

• Sorry still abit confuse. If the power is in minute, In this case, I have 32 kW of power in that minute, how can i convert to kWh? – SunnyBoiz May 1 '18 at 10:04
• kW or power represent how much energy you can create in an unit of time. – Long Pham May 1 '18 at 10:09
• "convert to kWh" You multiply it by 60, 1 hour = 60 minutes ?! – Long Pham May 1 '18 at 10:12
• So 32 kW * 60 minutes? Forget to mention this is POWER GENERATION not consumption if it makes any difference. – SunnyBoiz May 1 '18 at 10:15
• It's not that Power is in minute, power doesn't have a time component associated with it. If you produce or consume (there's no difference) a certain amount of power during a certain amount of time the product is energy. If your time is in minutes than you get Wattminutes (a rather unusual expression) if it's in seconds you have Wattseconds and if it's in hours you have Watthours... if it's in lightyears something went wrong! – po.pe May 1 '18 at 10:22

A kilo-watt-hour is one kilo-watt (1000 watts) used for the duration of one hour.

If you used 25,380 kW for one hour (that's a lot, something a very large factory or a medium town might draw), then you have used 25,380 kWh, and that is what you will be charged for.

If you were to use 1.2 kW (about a hair dryer) for a whole day, then you would use (1.2 kW)(24 h) = 28.8 kWh. Let's say you get charged $.15 per kWh. That means that leaving a hair drying running for a whole day costs$4.32 in this example. So save the environment and your wallet by making sure the hair dryer is off when you're not using it.

Figure 1. Energy is power x time.

25380 kW for one hour will transfer 25380 kWh of energy.

Note that's enough for 25 electric 2-car train sets. Are you sure you know what you're doing?

Figure 2. Each of these 2-car EMUs (electric multiple units) on the Dublin Area Rapid Transit has a power rating of about 1 MW. Source: WikMedia Commons.