Articles before measurements

[Jaro7788]

Hi, as most of us are aware, when talking about a particular speed, we need to employ the article "a" which is rather unusual and confusing (after all, logic would suggest that "a speed of 35 miles per hour" is pretty much defining). I also know that we talk about height and altitude using "a" (like in the sentence "the plane is flying at an altitude of 5,000 feet"). At the same time we would say "the age of 35 years".

Can anyone provide me with some general rule concerning the use of the definite article before measurement-concerned words, and when we should employ "a" or "an"? Or at least make a list of those words with the specified article so that they might be easier to remember.

[Mister Micawber]

First, 'a speed of 35 mph' is fine; so is 'the plane was flying at the altitude of 5000 feet'. They do not require a specific article. There is no particular association of the definite or indefinite article with terms of measurement, either, and there is no list of words that consistently take one or the other (though in English there are always idiomatic phrasings, of course — none of which spring to mind at the moment).

It is a matter of how the speaker/writer is thinking: if s/he is aware, is thinking ahead, that the defining phrase (e.g., 'of 35 mph') is coming, s/he may choose the definite article (the speed of 35 mph is inadequate to...'), but if s/he is thinking strictly linearly, s/she may choose the indefinite article for first-mentioned noun (a speed of 35 mph is inadequate to...).
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Native English teacher at Mister Micawber's