You Could Look It Up
Q. What is the proper way to write the commonly used speech abbreviation “twenty-four seven” (meaning 24 hours a day, 7 days a week)? Would one write “24-7” or “24/7” or something else?
A. All of the above. According to Merriam-Webster, the expression is spelled out “twenty-four seven” and can be abbreviated either “24-7” or “24/7” (the latter two are equal variants, which M-W separates by “or”). The entries for the spelled-out and abbreviated forms are separate in M-W, so you’ll have to make a choice. If you are spelling out numbers zero through one hundred (per CMOS 9.2), opt for “twenty-four seven”; if you’re spelling out only single-digit numbers (per CMOS 9.3), choose the first-listed abbreviation in M-W and go with that. There’s no harm, of course, in opting for the second-listed equal variant if that’s what you prefer, but whatever you do, be consistent—twenty-four hours a day, seven days a week.