I noticed that Potterverse uses the imperial system of measurement: 10 inches of parchment for a Transfiguration essay; Harry fell 50 feet from his broom; the dragon flew for miles it seemed; Hermione's rucksack weighed 35 pounds. Etc.

I researched both the imperial and metric systems and I know that the UK uses both the metric system and the imperial system, but I don't know how equally. Every time the subject has come up when I've been talking with someone from the UK or one of the European countries, that person has been staunchly pro-metric system.

Why did J.K. Rowling choose the imperial system for Potterverse?

Edited to Add: I'm looking for a quote -- verbal or written -- from J.K. Rowling or a reference from canon. I'm not asking this as a speculative question.

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    The UK really isn't very "pro-metric" at all, there's a definite lean towards the imperial here. Distances (for road signs, etc) are in miles, not kilometres; speed limits whilst driving are miles (not kilometres) per hour; weights are often done in pounds and ounces (and stones [1 stone = 14 pounds] when weighing people); milk is bought in pints (not millilitres); etc. I can't answer the actual question without speculating (which you don't want), but perhaps this will help. Apr 14, 2012 at 20:54
  • @AnthonyGrist - Thanks for letting me know about the metric versus imperial systems in the UK. This was helpful :) Apr 25, 2012 at 22:23
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    @AnthonyGrist You should not buy any milk that is not labelled in metric units. It's like to be over 10 years old.
    – Marcin
    Dec 10, 2013 at 20:40
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    As a Brit reading the HP books, I never noticed anything unusual about this. MANY people in this country (especially, but not only, older people) still use the imperial system in conversation, and all the examples you mention would be perfectly normal for Muggles to say in the UK.
    – Rand al'Thor
    Jan 13, 2016 at 21:34

3 Answers 3


On Pottermore, the post on Measurements says:

Just as British witches and wizards do not use electricity or computers, they have never turned metric. They are not governed by the decisions of the Muggle government, so when the process of metrication (switching to metric measurements) began in 1965, witches and wizards simply ignored the change.

Witches and wizards are not averse to laborious calculations, which they can, after all, do magically, so they do not find it inconvenient to weigh in ounces, pounds and stones; measure in inches, feet and miles; or pay for goods in Knuts, Sickles, and Galleons.


According to this page, the UK didn't start significant use of the metric system (outside of scientific use and international trade) until the 1960's. In keeping with the general theme that the magical world is slower to adopt newfangled changes (they still use a steam locomotive), they've stuck with the older system of measurement.

Out-of-universe, it also makes it more accessible to American readers with less editing.

  • It's my fault for forgetting to include this in my original post (which I have edited), but I'm looking for a JKR or canon source or quote. Otherwise, it becomes a speculative question, which isn't allowed. I'm definitely happy to consider any additional information if you find anything that is a JKR quote or from any of the 10 canon books. :) Apr 7, 2012 at 17:58
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    Speculative questions are allowed here. If you don't want speculative answers, that's separate.
    – cjm
    Apr 7, 2012 at 18:10
  • Thanks for that link -- when I read it I was reminded of this guideline. In this particular question I'm not looking for speculative answers. Again, if you find any canon information on this, please do edit it in. :) Apr 7, 2012 at 18:46
  • Do both the US and UK editions of the books use the imperial system? Apr 18, 2012 at 22:04
  • @KeithThompson -- Yes, it's imperial in both versions, UK and US. :) Apr 25, 2012 at 22:22

In short, she did it to spite her sister.

Rowling explains that she insisted on using imperial weights and measures rather than metric because she thought they were more quirky and thus more suited to wizards than the cold logic of the metric system. She subsequently accepted membership of the British Weights and Measures Association, not because she is opposed to metric, as has been assumed, but as a way of irritating her sister. "Di is never funnier than when infuriated, and among her many pet hates is the old-bufferish adherence to the old ways just for the sake of them."

Pottered history goes online as J.K. Rowling tells all


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