The phrase two-hour session should have a hyphen, because you are making a singular of what is actually plural, i.e. two hours.
But what about a one hour session? Should that be 'one-hour session'?

  • I don't think two-hour has a hyphen because it is actually plural but because it describes the session as would be the case with one-hour session.
    – jera
    Commented Mar 23, 2018 at 12:42

1 Answer 1


Because you are making an adjective out of the words one and hour, you should hyphenate. The combination of one and hour modifies the word session.

See a quick link here

And the Chicago style manual here, in particular page two

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