Hyphen In Compound Adjective With Fractions

When using a fraction (e.g. half or quarter) as part of a compound adjective, it should be hyphenated so the reader understands which fraction is modifying which noun.

I half-wanted to commit a felony.

A quarter-million dollars is still a large amount of money.

You’ll need one-third of a pound of flour and one egg.

Two-quarters are equal to one half, but one-half sounds smaller.

Three-quarters of his working hours are spent teaching mathematics; one-quarter is spent writing textbooks for elementary schools.

That’s a half-baked idea if I ever heard one!