# What is a kWh – kilowatt hour + CALCULATIONS 💡💰 energy bill

Hey there guys Paul here from TheEngineeringMindset.com. In this video we're going to be looking at what a kilowatt hour is. We're gonna cover kilowatt hours, watts, kilowatts, and joules, converting between watts and kilowatts, also how to calculate
your kilowatt hour usage with some worked examples towards the end. And lastly, how to calculate your monthly electricity bill. Now you've probably noticed
that your electricity bills will show you've been
charged for an amount of kWhs which we use, and when you buy electrical goods they are rated in Ws or kWs. Your electricity bill is rated in kWh, which means kilowatt hour. This is how much power was
demanded over an amount of time. Power multiplied by time equals energy, so let's quickly look at what a kilowatt is and then we'll come
back to kilowatt hours with some calculations, and this will make things a lot easier. On the electrical goods you purchase you'll see a value stated in W or kW, meaning watts or kilowatts. This is the power demand of the item, it tells us how much energy per second this will demand in order to work.

You can see this air heater
is rated at two kilowatts, and this light bulb is rated at 100 watts. Kilo means 1000, and
watt is a rate of power named after the engineer
called James Watt. To be precise, a watt
means one Joule per second, and a kilowatt hour equals 3.6 megajoules. What is a Joule? A Joule is an amount of energy transferred to do some work. Our food contains energy
rated in Joules or calories, and we consume this to
heat and power our bodies. But in this case a Joule
in electrical terms is the amount of energy dissipated as heat when an electric current of one Amp passes through a resistance of one Ohm for one second. If you want to learn more
on the basics of electricity then you can watch one of our other videos on how electricity works. The link is on the screen
now in the top right corner, or you can see the description box below. You can convert kilowatts to watts simply by multiplying by 1,000. So one kilowatt multiplied
by 1,000 is 1,000 watts. You can also convert watts to kilowatts simply by dividing by a 1,000, so 100 watts divided by
1,000 is 0.1 kilowatts.

To work out how much electricity
will be used by the heater we need to know how much
power it will demand and how long it will be switched on for. We can see that this item
is rated at two kilowatts. If you don't know the
power rating of an item, you can buy one of these
plug-in energy monitors which will tell you the volts, the amps, the watts, and also the kilowatt hours. They're pretty cheap and very easy to use, so I'll leave a link in
the description below, if you want one of these
then do check that out. Now back to the heater. So we want to know how many
kilowatt hours this will use. We know we can use the energy formula, which is energy equals
power multiplied by time. We also know that the power
is rated at two kilowatts and that this will run for three hours. So two kilowatts multiplied by three hours equals six kilowatt hours.

But what if the heat
only runs for 30 seconds? We can still use the energy formula, but because we're
invoiced in kilowatt hours we need to convert the seconds into hours. So there are 60 minutes and an hour and 60 seconds per minute. So 60 multiplied by 60, gives
us 3,600 seconds per hour. We can then convert the 30 seconds runtime into hours by dividing
the 30 seconds by 3,600. That means we will run for 0.0083 hours. So two kilowatts
multiplied by 0.0083 hours equals 0.0167 kilowatt hours. How about smaller items
when they're rated in watts? Let's say we have a 60 watt light bulb and it is switched on for 10 hours, we still use the formula energy equals power multiplied by time, but we need to convert
the watts into kilowatts, as we're invoiced in kilowatt hours.

So 60 divided by 1,000 is 0.06 kilowatts, and 0.06 kilowatts multiplied
by the runtime of 10 hours equals 0.6 kilowatt hours. If we want to calculate the cost, then we simply multiply the
kilowatt hour consumption by the electricity tariff set
by our electricity supplier per kilowatt hour. If we look at the heater fan, which is two kilowatts, and we run this for three hours, then two kilowatts
multiplied by three hours equals six kilowatt hours. Our electricity company
sells us electricity at 10 cents per kilowatt hour, so six kilowatt hours multiplied by 0.1 dollars per kilowatt
hour, equals 60 cents.

electricity consumption for the month? Well we need to create a table
for all the electrical items in the building, then we note down their power. Remember to quantify how
many of each item you have and ensure that each item
is rated in kilowatts. Then we need to calculate
how many hours per month they will be switched on for. From there we can calculate
the electricity consumption for each item using
the energy equals power multiplied by a time formula. Once you've done this for all the items, just add up the values
in the energy column and this will give you a total kilowatt hour consumption per month.

Once you know this you
can calculate the cost. Don't forget they will
likely be other costs on the suppliers invoice,
things like tax, etc. So you know if you need this in there, then you can build these in
separately to suit your needs. Ok that's it for this video, I hope you liked it and it has helped you. Don't forget to Like,
Subscribe, and Share, and if you have any questions leave them in the comment section below.

And also don't forget
to check out our website TheEngineeringMindset.com..