Cabinet Office gets its kilowatts in a twist

Visitors to the Cabinet Office website will see that this branch of the Government is measuring its energy use in “kilowatt-hours per hour”.  It is a sad reflection on the quality of civil service support given to this crucial part of the Government machine that such an incongruous and scientifically illiterate measure should be published.

If you go to the homepage of the website of the Cabinet Office (aka “Number 10”),, you will see in the right hand column an animated display headed “real time energy use”.  This oscillates between kg of CO2 per hour, £ per hour and (yes!) “kWh per hour”.  See extract below (or click on it for a clearer image):

As the website invites feedback (and promises a response),  I wrote on 27 December as follows:

“I wonder if you realise that the measure of energy used in your webpage (kWh per hour) is in fact nonsense.

The SI unit of energy is the joule (J).  The rate at which energy is used is power, for which the SI unit is the watt.  Thus 1 W = 1 J/s (joule per second).  Although it is in widespread use by energy companies, the kilowatt-hour is a somewhat unsatisfactory unit since it is energy divided by time multiplied by time. (In fact as there are 3600 seconds in an hour, a kWh is 3600 kJ (or 3.6 MJ)).

Your website then compounds the problem by dividing the unit again.  So we have energy divided by time multiplied by time divided by time!

Since what you are trying to convey is the rate at which energy is used (= power), the correct unit to use is the watt – or in this case the kilowatt. Thus the clumsy expression “Average 289 kWh per hour” should be simply 289 kW. This should be meaningful to readers as they will be familiar with electrical appliances such as kettles (which consume, say, 2 kW of power) and the output of power stations measured in megawatts (MW).

I would suggest that you amend your website to give more meaningful and scientifically correct information.

(BTW you should also leave a space between the number and the unit of measurement)”

As at 4 January no response had been received (but I will of course publish it if one does eventually appear).

The website does attempt to deal with the question of measurement units as follows:

“Why are you using these units and what do they mean?


We provide three different measures of the energy used: the amount of energy, its monetary cost, and the carbon impact of the energy used.


Energy use is measured in kilowatt hours (kWh), which are the standard units of a home energy bill (1kWh is the amount of electricity used by ten 100W light bulbs in one hour).


For electricity this number represents the amount of energy that flows into a building through the meter, and excludes distribution losses. For gas it is the amount of energy that is theoretically available by burning all the gas in an imaginary burner. For district heating it reflects a flow of temperature [sic] into the building over time (after the heat produced by burning the fuel has been transported to the meter, which involves other losses). So these numbers, while all being measured in kWh, mean very different things. This is one reason that we prefer to use ‘units per hour’ when combining them. In some ways it would be better not to combine them at all, because it implies that the measures are comparable. This is a global challenge though, and conventions have become established around combining kWh. So we’ll have to fix it another day…”

Comment: It is true (unfortunately) that energy companies measure energy in “kilowatt-hours” rather than joules, but there is no need for a Government Department to implicitly endorse this practice. In any case, it does not excuse the obvious error of multiplying by a unit and then dividing by the same unit.  Even the most scientifically-challenged should be able to see that.  Perhaps it is just an untypical error by a junior civil servant (I hope so), but one wonders why it wasn’t spotted by a scientifically aware colleague.

20 thoughts on “Cabinet Office gets its kilowatts in a twist”

  1. I agree this is a very sloppy article such as we can expect from any government department.
    However, I agree with Bob above, the kWh is used worldwide for standard energy measurement and as every meter around the world would need to be changed from kWh to joules there could be a bit of a lead in time. I am not surprised that Australia leads with joules apart from Germany which also tends to react swiftly to SI units.
    This in no way excuses the use of kWh per hour which is just plain stupid, as is 1 kW being referenced to 10 x 100 W light bulbs which are no longer legal for trade and used by very few people. 1 kWh is equivalent to one thousand watts being consumed for one hour, quite irrelevant if you are using LED lighting of just a few watts. They could have made the connection between gas burning and joules, then reference that to the electricity in kWh, that way round it would make more sense. On the plus side, there are no “homes” mentioned!


  2. Even though we have all grown up with the watt, it still presents many of us with a problem. That is because we are accustomed to rates being expressed as some tangible thing per something else, for example pounds per square metre (for carpet pricing), BTUs per hour (for boiler output), litres per second (for burst water mains), thousands of pounds per hour (for the takings at Harrods sale) and so on. The idea that one word can express a rate, as in one watt is one joule per second, may be difficult for some of us to get our heads round. Would it help if we tried to master one measurement system, rather than acquiring a passing knowledge of two?


  3. Bob’s link to Australia shows:
    ” It is listed on your bill as cents per kilowatt hour (c/kWh) for ELECTRICITY and cents per megajoule (c/MJ) for GAS.”
    [I put them in CAPITALS for emphasis].

    Why not both in SI units?
    The UK government intends to have a mass roll-out of Smart Meters.
    I think the report of the Government’s technical specification for Smart Meters may be due to come out soon, see:

    Will customers have the opportunity to see their energy use (for gas and electricity) displayed in SI units? Probably not!

    Now a question for readers who know about the top of the range smart meters that are available in other countries; can they be made to display only SI units?
    If SI meters suitable for domestic homes are commercially available perhaps it will be useful for us to forward details of them to our MP’s.


  4. I have now received a reply from the Cabinet Office website – as follows:

    “Thank you for your feedback! We appreciate that you took the time to write in.

    Absolutely – kWh per hour is – as you have noted – synonymous with kW, and less concise. We actually changed the metric from kW in response to user research that exposed a side effect of using the more common scientific language: non-experts frequently leapt to the incorrect assumption that kilowatt hours is a flow (we believe this is due to a totally reasonable heuristic – it sounds like miles per hour and other common expressions of flow), when in fact it is an amount, like miles. KWh per hour is more verbose, but still correct (although it has some inelegant redundancy in it). But it turns out this makes it easier for non-experts to understand without assistance and and it allows us to express money, carbon and energy all in a comparable form. For expert users, we share your preference for sticking to the SI units – after all that’s the agreed language for scientific communication.”

    Essentially, they are saying that they dumbed it down in order to make it comprehensible to people with limited understanding of measurement units. What a condemnation of 40+ years of metric education!

    An alternative approach – admittedly a long term one – would be to improve the way that measurement units are taught in schools. Discouraging the use of obsolete units of measurement and their accompanying conventions would also help.


  5. @Wilfred

    The use of a one word name for compound units outside scientific circles is not unprecedented. qv the knot for the speed of ships and aircraft.


  6. Whilst we’re on the subject of strange or stupid units, I just became aware today of the U.S.A’s latest attempts to mess themselves up (and probably everyone else too) by their invention of the “MPGe” (see

    This is the “miles per (U.S.) gallon equivalent” to be used for expressing fuel economy on electric cars. I can imagine our friends at “Top Gear” are busy inventing the U.K version as you read this!

    Just out of interest, what *is* the most concise way to express fuel economy of non-fossil-fuel vehicles in S.I. units? Metres per Joule would seem to be the most fundamental, but that ignores the amount of acceleration needed to actually achieve any useful velocity out of the vehicle. I notice that the few times “Top Gear” and the likes have reviewed electric cars, they’ve normally limited the discussion to things like “range from a full charge” and “how long does a full charge take”. Both valid metrics, along with top speed and (in the case of sportier cars like the Tesla) 0 – 62MPH time. (Well it *is* Top Gear after all, they couldn’t be caught dead claiming a 0 – 100km/h time now, could they?)


  7. Shame that the Cabinet Office response had to include miles, and not kilometres.


  8. @Wild Bill

    I bring you the MPIGe, miles per Imperial gallon equivalent. Just multiply by 1.2. I see the US labels also include a supplemental kWh/100 mi rating (using US abbreviation of “mi” for mile). Frankly that would work for both of us, as it connects directly to electricity pricing.

    Any measure of fuel economy (or efficiency) is inherently measured over a specific drive cycle. Drive a different drive cycle, get a different result. The US city and highway drive cycles do not agree exactly with their analogous European drive cycles, so comparison is more than unit conversion. (There are actually 5 US drive cycles now, averaged in some way to yield the classic city and highway economies)

    You have to decide whether to measure distance /energy or energy/distance, but you have to realize it is total distance and total fuel energy over a specified drive cycle. You could convert mpg to feet per minim, but that wouldn’t make it valid over the first foot travelled, it’s an average.


  9. @Wild Bill That link did not work for me, try
    An interesting one, I wonder how metric countries handle that. It is almost certain that UK will adopt this unit, probably with the US gallon as well, as we no longer have one of our own.
    As our PM said, we are running on a full tank of gas. Let us go the extra mile and not run off the road now.


  10. @John Steele
    I am sorry to conflict with your good self, but I thought this was a “lets go metric” site!
    The real big problem I have with this one is that the UK does not use the gallon (apart from the media of course), and has not done so for around 30 years, it is no longer a defined unit as far as I know. We do not need a new mpg unit in any form what so ever, no doubt we will get it none the less. I would be a bit happier if a miles per litre equivalent was proposed, but not much. We do not use metres on the road either, but j/m sounds good to me, so just for a bit of fun lets try this.
    From the above link, 1 US gall (gas-petrol) = 33.7 kWh.
    From my calculations this comes to near enough 32 Mj/l. (33700W*3600s/3.78L)

    From this a Ford Fusion rated at 108 (mi)pg e = (108mi*1.6km/3.78L =45.7 km/l e) = (45700 m/32 Mj) = 700 j/m e. Now I have probably got that all wrong, but someone will work it out properly for me. My car works out at around 4500 j/m, not very good!


  11. @BrianAC,

    I would expect metric countries to use kilowatt hours per 100 kilometers.
    Note from above, the US uses kWh/100 mi as supplemental info.

    I can accept MPGe as a way to deal with alternate fuels, which have different energy content, especially in vehicles which are flex fuel. It seems dumb for electric cars. The whole concept of equivalent gas mileage seems dumb for hybrids that are part electric, part gas. The electric range highly distorts the fuel economy, and gives NO idea of what to expect when the battery range is exhausted and the car starts its engine. They should give separate electric and internal combustion ratings.


  12. The reason for the apparent clumsiness is possibly that although the government are allowed (indeed expected) to use plain English for most written exchanges with the general public, that common sense and inclusive approach is not used (and is probably not allowed) where units of measure are concerned.

    So where the majority of the British public would probably be more comfortable with logical, familiar and understandable terms such as Btu and Btu/h, the effect of the various EU directives is that the government copy writers are simply not allowed to use those “plain English” terms, and instead have to try and couch what could and should be easily understandable, in unfamiliar metric system units, as best they can, and using illogical and inflexible symbols to portray them too.

    That is why, outside of the major supermarket chains, purveyors of fruit and vegetables in much of the UK still display the price of potatoes, apples and tomatoes primarily in GBP/lb and then, but only if they need to kowtow to the trading standards office that day, the more often than not, much smaller and less legible: GBP/KG, GBP/kg, GBP/Kg, GBP/kilo, GBP/g, GBP/gm or whatever.

    The fact is, and this is the pill that many here still need to swallow, that the British public will not be told what units they have to use, and after they have chosen what units they want to use, they will not be told that there is a right way and wrong way to write its symbols. Over time, general usage will eventually stabilise, and a standard form will emerge, but it won’t necessarily comply with every nuance of the SI brochure.


  13. @CharlieP
    The majority of the British public wouldn’t have a clue what units like BTU and BTU/h are. They’re not familiar or understandable and they’re certainly not logical.
    You say that the British public will not be told what units they have to use or how to write the symbols of those units like it’s a good thing. What is your problem with delivering or receiving information that has been taught in schools for the past 40 or 50 years and is understood and written in practically the same way in almost every country on Earth? Do you believe the rules of spelling or punctuation should also be left to personal preference? Would you see is as a positive thing if the British public refused to be told how to spell or punctuate? Language and measurement are both forms of communication. The UK is officially a metric country so all communication with the public should be in SI units and the units should be written in the correct form just as the spelling and grammar should be correct and in Standard English.
    If the public don’t understand either they should learn. There is nothing noble about ignorance.


  14. @Cliff

    You are attacking the messenger there: and that will not change the reality; that the British public will not be told what units they have to use or how to write the symbols of those units. You are also insulting the British people by characterising their affinity with their cultural identity as “ignorance”.

    The people of England have been a free and independent people, and in that country, for more than one-thousand years. The result is a long and proud history and a mature cultural heritage rooted in a set of traditions and customs that have evolved over that period.

    That cultural heritage will not we wiped out or overridden by teaching the children of that proud heritage new ways of doing things, even if they are “better” ways, and even over a period of fifty years.

    The English measurement system has evolved as part of that heritage, in the same way that the English language itself has. Do you think that the British would be amenable to the suggestion that they substitute their use of English in favour of French as their everyday language, even if their children were taught it, and not English, at school?

    Being proud and protective of their cultural heritage and identity is something that is encouraged and supported in most other cases: would you ruthlessly deprive the British of theirs? Should a government, do you think, be encouraged to communicate with their citizens in the natural language that their people understand, or in a new contrived language which is more scientifically and mathematically cohesive? If the latter, then would you also support replacing all the world’s spoken languages with Esperanto too? If not, why not?


  15. @CharlieP
    Technological inovation is also part of the British people’s cultural identity and heritage. In fact British scientists and mathemeticians were instrumental in developing the metric system and several metric units are named after them.
    Measurement is a science and has nothing to do with cultural identity. No other country that changed from traditional measurements to the SI system has suffered from a loss of cultural identity and to suggest that it has is insulting to 95% of the countries in the world. To harmonise measurement systems across the world creates a bridge of communication like sport. To retain parochial measurement prevents the proper understanding of the universal system and creates unnecessary barriers between different cultures. You ask if I would support a universal language like Esperanto replacing English? Of course not, you cannot compare language and science.
    I’m all for keeping good British traditions like scientific innovation, tolerance and pride in workmanship but doggedly preserving an inefficient science is a bad tradition like the class system and should be disposed of.


  16. @CharlieP:

    You are quite mistaken that the British people will not be told what measurement units to use. Thay have been told that even since the Magna Carta, which was very specific in saying that there shall be only ONE [my emphasis] way to measure wine and a whole lot of other items. That dates from the mid-1200s, a period of over 850 years. Then, in the early 1800s, those measures were changed again, and STILL the British people were told what measurement units they have to use – and they used them.

    All that is happening now is that we need to continue that process and move on again, by using the same units that 95% (yes, you read that right – 95%) of the world’s population uses not only in science and commerce, but in everyday usage as well. We are the odd ones out, and our persistence in using imperial makes us look stupid in the eyes of the world – I have friends, colleagues and family spread around the world (primarily Canada, Australia and South Africa) who ridicule this country for its archaic roadsigns. You might like to be ridiculed by the rest of the world – I don’t.

    As for maintianing our heritage – what heritage? Fahrenheit was German, the mile was Italian (from the word miglia), and the pound was also Italian (from libra, abbreviated to this day as lb.). Nothing English about that lot. Conversely, the modern SI temperature scale, using kelvins, was invented by Lord Kelvin, a great British scientist. Bishop John Wilkins submitted to the Royal Society a proposed linear measurement scale that was divided into tens, and corresponded closely to today’s metre. The French were quick to adopt it – the British, in their bumbling way, weren’t. Nonetheless, the beginnings of the modern metric system were created in THIS country, and we should be supporting it (it is part of our culture, after all), and not continuing with various German and Italian measures – ones which those countries thenselves have long abandoned, because they didn’t make any sense in the modern world.

    Many countries once had their own forms of measurement, and have since abandoned them in favour of the metric system, without losing their heritage and culture. Is Japan any less Japanese when it adopted SI? Russia? Sweden? Is Australia any less Australian since it went metric (and highly succesfully)? No, of course not, and for you to suggest that Britain will lose its culture and identity by going metric is a falsehood. As has been shown in the past (and as I pointed out above), this country has a long history of changing its measurement units as better ones came along, without becoming any less English (or British) in the process.

    You mockingly suggest replacing English with Esperanto. If Esperanto was spoken by 95% of the world’s population, then yes, there would be a case for it. As however there are many major languages in the world in active use (and many minor ones spoken in small pockets of population), that is an invalid analogy.

    Our economy is very fragile. Our children need to become metric educated (and metric using) adults in a fast moving and highly metric world if they are to have any kind of a future. Saddling them with complex, incoherent, and above all, OBSOLETE, measurement units is disadvantaging them in this world. You CharlieP seem to like to live in the (long gone) past. I prefer to look to the future.


  17. @CharlieP
    Avoiding the risk of a rebuke from the moderators, all I can say to this is “what a load of twaddle”.
    Firstly I have no idea what a btu is or ever was (please good folk do not tell me, I do not need to know!). This despite it being on my gas bills from the 1970’s, and on various gas boilers. It was one of these quaint (?) (as some would say) UK measurements that meant absolutely nothing to anyone except those who really needed to know. It you know then you must be a gas fitter or some such. Much like the current “unit of alcohol”, oft used but seldom understood. So where you dragged that up from I have no idea. Thankfully they started using kW and kWh instead. Now we can compare our gas usage with our electricity usage in the same units. We get charged in the same units for gas and electricity, so we can compare costs also, how you see that as a bad thing is beyond reason.

    I have to admit I seldom shop outside of the local supermarket and the internet. However, I do watch all the news and see many high streets and market shots therein, I am sure that if many outlets sold mostly in lbs and pints or whatever I would notice. and so would the good folk here. I admit I have seen it in a local butchers shop before it closed down, no connection of course. I have seen little evidence of mass sales on the internet in “stupid units”, but it could do with a lot less supplementary inches or whatever from my point of view.

    Now, the great British public, like that does not include the likes of us here? You say we will not be told what units to use. Well, explain how any society can live together if each person uses a different unit to everyone else. How would they communicate? Your viewpoint is without reason. Of course we all have to use the same units otherwise trade becomes difficult or impossible.

    I do agree that on a personal level it matters little what symbols to use, so long as it is understood. However, government and large stores should follow strict rules and set a good example to all of us so we can all “sing to the same tune” and fully understand the subject.

    Maybe you need to read a bit of history, about the Vikings, Romans, 1066 and all the rest that have raided and brought good and bad to this country. Where do you get the impression that this forward step of metrication is somehow from outside influence? Have you read the government select committee report of 1862? That clearly defines the measurement muddle, what terrible external power forced that upon us?

    [This thread of the discussion has departed considerably from the original article and has probably run its course. So let us draw a line here. Further “on-topic” comments are of course welcome – Editor]


  18. CharlieP,
    The English forced the Scots to replace their native measurements with English units by the Treaty of Union with England in 1707. Are you suggesting that Scots are not proud or independent people that have suffered a loss of identity from that action?


  19. Do I correctly understand that the new EU lightbulb label
    requires labeling with the unit xxx kWh/1000 h and no mention of lumens except for the efficiency required to achieve the letter grade?

    That seems “uninformative.” Don’t you want to know first and foremost how many lumens you get and secondly, the power requirement? Obviously kWh/1000 h reduces to just watts, maybe average watts measured over 1000 hours, but what is the point supposed to be for this cumbersome measure? I’ve seen images of the older label and it seems a LOT more useful.


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