21

Why don't we measure electrical consumption in joules, instead of kWh? Aren't they the same measurements, but one is more "proper"?

Kortuk
  • 13,412
  • 8
  • 62
  • 85
Thomas O
  • 31,786
  • 58
  • 184
  • 322

3 Answers3

18

Yes, they're the same thing, but, an electricity bill stating n * 3.6 megajoules is a bit abstract compared to Watthours when light bulbs are rated in Watts.

Toby Jaffey
  • 28,836
  • 19
  • 98
  • 150
  • 5
    +1! Just what I was about to post. Also, why megajoules PER HOUR? Electricity is usually charged per energy consumed (so joules with no hours), per installed power (so watts or VAs) or per peak power (again W or VA). Also, it's not watt/hour, it's watt*hour. – AndrejaKo Mar 14 '11 at 13:31
  • quite right, wasn't thinking straight – Toby Jaffey Mar 14 '11 at 13:42
  • 6
    I've just eaten a Caramel Wafer - 134 kCal it says on the wrapper. I just worked out that this is 0.156 kWh. I feel much healthier now :) – MikeJ-UK Mar 14 '11 at 14:21
  • 2
    Please note that when measuring the total energy used, you are measuring WattHours, not Watts per Hour – James Mar 15 '11 at 12:05
  • Quick! How long does it take to drive to a city 275 km away, at a speed of 15.3 m/s? Oops ... – Kaz Apr 21 '13 at 20:45
  • 2
    This answer doesn't really make sense. Watts is joules per second, it makes more sense to use joules. Using kWh is a lot like measuring distance in kph days. The only reason I can think of to use kWh is the scale of the unit fits better on bills – MikeKulls Mar 01 '18 at 02:25
7

Kilowatt-hours makes more sense to the non-physicists. For instance, business and marketing types who set the prices for pushing electrons to you.

DarenW
  • 4,060
  • 1
  • 25
  • 37
  • 3
    It really doesn't make more sense. You are billed for each bucket of energy you use, so why not report that in buckets, and label light bulbs by how many buckets they use per hour? Reporting energy usage in buckets-per-hour-hours is not simpler. – endolith Jun 29 '11 at 15:13
  • 1
    @endolith: It makes more sense to the average consumer. Light bulbs and other appliances are rated in Watts, and hours is a convenient unit to describe how long the appliance was on during the billing month. A 1 kW hair dryer run for one hour is going to cost 1 kWh on the electric bill. KilloWatt-hours and Joules are both valid units of energy, but the first has more direct relevance to the average consumer and is therefore simpler. – Olin Lathrop Oct 10 '11 at 21:57
  • 1
    @OlinLathrop: Measuring energy in kJ and power in kJ per hour would make a lot more sense to the average person. You think gallons per day or miles per hour are confusing to laymen? – endolith Oct 10 '11 at 21:59
  • @endolith: I think a lot of people don't know from Joules. Joules isn't more right as a unit of energy than kWh just because you might use that as a electrical engineer. Joe Sixpack is used to kWh, so I don't think it's a good idea to change it. – Olin Lathrop Oct 10 '11 at 23:38
  • kWh may make more practical sense but I cringe (and get confused) when people give "yearly consumption" in kWh/year. Why don't they use power units? – Oskar Limka Nov 30 '23 at 10:38
-1

I agree w/ Olin about using units that make sense not only to the average consumer but kWh makes sense to everyone. I'd like to add: a kWh does not equal a kJ. A kWh is equal to 3600 kJ.

gman
  • 190
  • 3