few, fewer, less, lesser

Use few to mean an indefinite small number whose size depends upon the context:

for example, among U.S. citizens a few may number in the thousands

Use fewer only with a plural noun for things that can be counted one by one:

fewer than 10 men

fewer chairs

Do not write fewer in number.

Use less with a noun that does not have separately countable parts:

less water, less activity, less money.

Also use less with a plural noun that is a mass, a measurement, or a total, especially in expressions following less than:

less than two hours

less than $30

less than five miles

less than three gallons

a total population of less than five million

less than 10 percent of them are now nomadic

less than half of all Roma children regularly attend school

Do not hyphenate less or lesser in compound modifiers:

a less useful book

the lesser known of the two