Usage The adjectives less and fewer have similar meanings but are used in slightly different ways. Fewer is used with nouns that can be counted.

classrooms with fewer students

They have fewer than three children.

Less is usually used with nouns that cannot be counted.

He makes less money than she does.

The new model uses less power.

But less is also more likely than fewer to be used with count nouns that refer to distances and amounts of money.

an investment of less than $2,000

It's less than 100 miles away.

Less is also used in mathematical expressions and in certain phrases.

an angle of less than 180 degrees

Write it in 25 words or less.

It is also used instead of fewer with other sorts of plural nouns, although many people still consider this use incorrect.

Less than 10 people showed up. = Fewer than 10 people showed up.

《韦氏高阶》less 词条下的用法提示。