Hyphen In Compound Adjective With Numbers

When numbers are used as the first part of a compound adjective, they should have a hyphen connecting them to the noun which follows them. This way, the reader knows that both adjectives are being used to modify the noun.

This applies whether the number is written in words or in digits.

The president of the company gave a 10-minute speech to the Board of Directors.

He is knowledgeable in thirteenth-century politics.

The boy threw a rock at the second-story window.

N.B. A hyphen is not required if the number is the second word in the compound adjective.

He is a victim of Type 2 diabetes.

This elevator doesn’t go down to Basement 3.

A hyphen is not required in this compound modifier because the number is the second element in the compound adjective.

As well, you won’t need to hyphenate if the number is the only adjective.

We live on the second story of an old house.