The conventional rule for correct usage of less and fewer is simple: less applies to singular nouns (including mass nouns), and fewer applies to plural nouns. There are plenty of exceptions, however, and using one in place of the other is not a serious usage problem, especially in informal contexts. In formal writing, it’s probably best to honor the traditional distinctions just to be safe.
Examples
According to the conventional rule, these would be incorrect:
Although it is a maximum-security facility, less than 144 minimum-security male inmates are kept there . . .
Less players, less schools giving out scholarships. [Lax Magazine]
ten items or less
Less people working means less need for work uniforms … [Investor Place]
There are exceptions. In measurements of non-discrete quantities such as time, space, or money, less is not considered incorrect—for example:
With less than 45 seconds on the clock … [Glasgow Daily Times]
A one-way fare costs less than $50 … [Whig]
Low voltage electricity (less than 500 volts) does not normally cause significant injury to humans. [Journal Gazette]
In past years, that figure would have been less than 20 percent, he said. [Chicago Sun-Times]
One less
Because fewer only applies to plural nouns, there is nothing questionable about one less—for example:
If they held one less seat, there would be no choice but to win over a Republican … [NY Times]
And while this use of one fewer isn’t necessarily wrong, it might strike some readers as overcautious:
That leaves him with one fewer social connection, and that much closer to himself lapsing into loneliness. [Boston Globe]
