BYU recommends following Chicago’s alternative numeral rule (as outlined in 9.3) with these clarifications and modifications:
Spell out one through nine, and use numerals for 10 and above, unless context dictates otherwise.
Treat numbers consistently for the same type of item within a sentence even if one is below 9 and the other is above 10; in such cases generally use numerals, unless the context would dictate otherwise.
We have 7 cats and 12 dogs.
Following AP style, BYU recommends numerals for units (dimensions, sizes, percentages, temperature, speed, money, age). Please note the difference between dimensions and distances and between ages and time.
The 5-foot-tall girl ran five miles.
The 5-year-old boy slept for five hours.
Use numerals in headline text.
For phone numbers, divide numerals using two hyphens instead of parentheses or periods.
801-422-2222; not (801) 422-2222 or 801.422.2222
In accordance with Chicago 9.37 and in contrast to the recommendation about numbers above, spell out the hour when written with o’clock.
When written with p.m. or a.m. use the numeral.
Include :00 only when other times in the surrounding text are written with minutes.
The meeting started at either 6:00 p.m. or 7:30 p.m.
The train arrives at 6 a.m. on Mondays and 7 a.m. on Tuesdays.