Metrication Dilemma

Thu, 08/15/2019 - 02:35

This may well be a purist’s dilemma, however there is nothing more confusing, and consequently, frustrating, than seeing stats like the following: ‘Fuel economy of 23.5mpg and 280g/km of CO2’. Most descriptions of car specs and articles directed at the British market will present exactly such a jumble of imperial and metric measurements. In attempting to cater to the more old-fashioned reader however, are authors making stats less rather than more accessible to their audience? And what is the alternative?

The units this article is chiefly concerned with are those for speed, fuel use, CO2 output, and torque.

First of all the question must be as to the extent to which unit confusion could be avoided at all. There is a fundamental discrepancy of units between the UK and the Continent – the use of miles rather than kilometres for the measurement of distances.


With this accepted as a given, it follows that measurements of speed must also refer to distance in miles. It would make little sense to present British readers with top speeds for their cars in kilometres per hour – especially as the conversion rate of 0.621371192 miles to the kilometre is far too unwieldy for quick and convenient conversion. Measurements of speed must be oriented around measurements of distance in order to provide readers with a ‘feel’ for the actual speed of the car, i.e. to enable them to imagine and judge data in accordance with every-day life.

This same argument can be used in relation to measurements of fuel efficiency. The average Briton will not care about the fuel efficiency of his or her car in litres per 100km, and instead demand to know the value in miles per gallon. This puts fuel use into the context of miles driven, thus allowing readers to apply specs to a real-life situation.

Looking at the example of ‘Fuel economy of 23.5mpg and 280g/km of CO2’ however, the same argument as detailed above does not seem to be commonly applied to measurements of CO2 output. It may be because the significance now attributed to this value is a relatively recent development; however the use of kilometres in reference to it does raise questions. Is CO2 output in g/km a value considered important by authors and readers, or simply one tagged onto the list of car specs? Alternatively, could the fact that the values for CO2 output have never been translated into a miles-related unit mean that authors and readers alike have managed to become accustomed to and learned to interpret CO2/km? If so, could this be used as an argument to present all data relating to cars (including maximum speed fuel efficiency) with reference to kilometres, to avoid all current unit confusion?

The truth, perhaps, lies somewhere in between. Whilst British customers have learned to recognise the CO2/km value provided in lists of car specs, it is unlikely that most will understand it in that strict sense. Due to the lack of comparative miles-values, Britons have learned to compare CO2 output between cars, and thus judge values as relative to one another. It is however unlikely that CO2 output is judged by most British readers as a value in and of itself – if a kilometre is not a value that most can relate to, then CO2/km will remain an abstract number to most readers.

Does this comparative view present a problem? Many manufacturers’ websites, for example provide details about its models in metric measurements only. The change in the measurement of torque from lb/ft to Nm was a move towards a more abstract unit, which has now been widely accepted. Could the same apply – in time – to CO2/km? To what extent does it already apply? Are we even concerned with CO2 output other than in its relation to tax?

This unit confusion is not purely a purist’s dilemma. While we are getting better at judging the length and width of vehicles in millimetres rather than in feet and inches, the fact that miles-related units have remained in use for the measurement of distances and speed shows that it is important for readers (and potential customers!) to be able to relate the information conveyed to every-day situation. Does this apply to CO2 output?

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