- for each; during each
- Double rooms with full breakfast are £40 per person per night.
- The preposition per is usually followed by a singular noun phrase with no determiner.
- Take one pill per day, not *Take one pill per a day, and not *Take one pill per days.
- It is sometimes followed by plural noun phrases, almost always after numbers such as 100, 1,000, 100,00, etc.
- The rate has dropped from nearly 30 per 1,000 women of childbearing age, to less than 2.