It is not only learners of English who confuse less and fewer – some native speakers also frequently use them incorrectly.
But less and fewer are not actually so difficult to use correctly: less means ’a lower amount’ (menor cantidad de algo), while fewer expresses ‘a lower number’ (menor número de algo).
In other words:
- fewer and less are both the opposite of more;
- we use fewer with countable nouns; Fewer con nombres contables
- we use less with uncountable nouns. Less se usa con incontables.
- I’ve got less time than I had last year. (time = uncountable noun)
- He’s got less money than his wife. (money = uncountable noun)
- Low-fat milk has fewer calories than full-fat. (calories = countable noun)
- The government built fewer houses last year. (houses = countable noun)