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Pluralization rule for “five-year-old children”, “20 pound note”, “10 mile run”

Is it correct to say

"This is a forty foot drop"


"That is a forty foot telescope"

Shouldn't it be "forty feet"?

And what if it is

"This is a thirty nine foot drop"


Are both correct? Does it depend on the context? How does it work?

  • Does it depends on the region? I heard Bear Grylls ( en.wikipedia.org/wiki/Bear_Grylls ) say 40 foot drop, he was born in UK.
    – BrunoLM
    Commented Jun 3, 2011 at 19:01
  • 1
    Are there any multi-linguists among us who can say whether this counter-intuitive 'singularisation' occurs in other languages? Commented Jun 3, 2011 at 20:05
  • You can read here all about the Forty Foot Drain Commented Jun 3, 2011 at 21:08
  • 1
    @FumbleFingers: For the length scale you would say (singular) "Vierzig Fuß" in German instead of "Vierzig Füße" (plural), too, except usually the metric system is used. Also 7 Euro and not 7 Euros is used (except when there are 7 single Euro-coins). But a "5 Jahre altes Kind" contains "Jahre" (years), not "Jahr" (year), and a "10 Meilen Lauf" uses "Meilen" (miles) instead of "Meile" (mile).
    – Stephen
    Commented Jan 12, 2012 at 20:08

1 Answer 1


The forty-foot drop is correct.

Compare this:

1) He's a 10-year old.

2) He's 10 years old.

In the first example, a 10-year old stands as a noun (notice the article preceding it). In the second example, it's not a noun, therefore no article.


1) It's a 40-foot drop.

2) This drop is 40 feet in height.

  • 1
    William Safire has a great article on this, published in "What's the Good Word." He notes that in constructions like "toothbrush," adjectival modifiers are normally singular.
    – The Raven
    Commented Jun 3, 2011 at 19:10
  • Very nice answer, thanks. And thanks @The Raven for this info, its very nice to know it.
    – BrunoLM
    Commented Jun 3, 2011 at 19:21
  • would "This is a forty foot drop" and "This is a forty foot deep drop" change this?
    – Andrey
    Commented Mar 15, 2018 at 16:37

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