Less and Fewer

We use less to describe the quantity of something. Usually we use less with uncountable nouns.

Sam drinks less coffee than Paul.

Coffee is uncountable; we talk about the quantity or amount of coffee (a cup of coffee, a litre of coffee).

We use fewer to describe the number of items. We use fewer with countable nouns.

Paul eats fewer biscuits than Sam.

Biscuits are countable; we talk about the number of biscuits (2 biscuits, 10 biscuits).