fewer vs less

Fewer modifies plural countable nouns, while less modifies singular uncountable nouns.

• fewer

  a smaller number of countable items

  The express lane is reserved for customers with ten fewer items than usual.

• less

  a smaller amount of uncountable mass

  Adding less sugar to your coffee is a simple way to reduce daily calories.

• Wrong: There are less chairs in this classroom than we actually need.→Right: There are fewer chairs in this classroom than we actually need.

• Wrong: I have fewer time to finish this project than I thought.→Right: I have less time to finish this project than I thought.

Fewer is for things you count; less is for things you measure.