I've just read this in a review:

Thankfully, the energy efficient Qualcomm chip helped the handset reach a best-ever score of 17 hours and 30 minutes in our continuous video rundown test. Compared to the outgoing model, which lasted ten hours 43 minutes in the same test

The first part uses 17 hours while the second part uses ten hours. Which is correct? What are the rules to determine when which should be used?


A common convention (used by The Guardian style guide — see "numbers") is to spell out the natural numbers nine and below, and use numerals for natural numbers 10 and above, and for any non-natural numbers (decimals, negative numbers, etc).

(Updated: should be nine and below, not ten and below.)

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  • Yes, many style guides specify where the border should be. – andy256 Apr 14 '14 at 9:00
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    Not so nice when writing 'she was around nine or 10 years old' - 'she was around 9 or 10 years old' or 'she was around nine or ten years old' are better than the first (in my opinion). In the OP example I would prefer to see '... 10 hours 43 minutes' – Frank Apr 14 '14 at 9:06
  • True. One needs to note that style guides are just that — guides. It is important to take context into account. – tobyink Apr 14 '14 at 10:20
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    The way I learned it, numbers twelve and below are written out, numbers 13 and above are written as digits, in the general case. (Frank’s example shows an exception to the general rule.) – mirabilos Apr 14 '14 at 10:42
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    Numbers at the beginning of a sentence are usually spelt out. – Wayfaring Stranger Apr 14 '14 at 11:22

Generally the guideline is to choose a small number (in this case 10), and write it and smaller numbers in full, and use numerals for larger numbers.

And be consistent.

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    However, as Frank illustrates above, applying a strict rule-based consistency can produce an inelegant result. In the instance he cites, my own preference would be to prioritize the internal consistency of the numeric pairing. – Erik Kowal Apr 14 '14 at 9:20

As a rule of clear expression, things that people compare should be directly comparable. Use the same format for both.

Therefore regardless of whether you'd write "10 hours" or "ten hours", you should write "17 hours 30 minutes or 10 hours 43 minutes" not "17 hours 30 minutes or ten hours 43 minutes".

Of course any combination is grammatically correct, this is therefore a question of style. Someone else might put more priority on consistently writing "ten" than they do on the internal consistency of the sentence.

Personally I don't think I'd write "ten hours 43 minutes" anyway. Once I start using numerals in a sentence, I stick with them. Exceptions occur where the quantities aren't "the same thing". So:

I have 3 donuts, my colleague has 12.

Two of the three of us are human, the other one is 12 squirrels standing on each others' shoulders in a long coat.

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    I think your first counter example is typoed, "17 hours 30 minutes" should be "17 hours thirty minutes" – Richard Tingle Apr 14 '14 at 11:07

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