What to Know
Generally, fewer is used when the number of things is counted (“fewer problems”) whereas less is used when the number is measured (“less trouble” or “less time”). However, this is not a strict rule and there are accepted instances of less being used with countable amounts such as “250 words or less,” “3 items or less,” and especially with money (“less than $20”) and distance (“less than 3 miles”).
I am hearing more and more people use the word ‘less’ in situations that require the use of the word ‘fewer’. It bugs me to no end. Its fewer cars not less cars. Fewer doctors not less doctors. If you can count the thing, then you use the word ‘fewer’. It that simple. The two words are not interchangeable. Its not that hard.