Less and Fewer

Two properties distinguish when to use less and fewer in English.

Use less if it's measured by mass, for example, less sugar, and fewer if the nouns are countable, for example, fewer sugar cubes.

Use less if the nouns don't go plural, for example, less furniture, and fewer if the nouns pluralise ok, for example, fewer chairs.

Hopefully, this will help clear up any confusion.

Also see: Affect Effect; stationary stationery; Compliment complement, the pedants are revolting (reddit)