First, according to Alred’s Handbook of Technical Writing, When we write about measurements, we should always express the units of measurement as numerals.
If the measurement is one or less, use the sigular form of the unit.
(His scar was only 0.5 inch long; I still refuse to walk even 1 foot toward him).
If the measurement is more than one, use the plural form of the unit.
(Her new tattoo is 1.5 inches across her cheek; please stay 3 feet away.)
If the measurement is describing something (functioning as an adjective), add a hyphen and the singular form of the unit (a 1-inch bandage, a 30-foot yacht).
So how we write it depends on how we are using it. That’s my story, and I am stickin’ to it.