When a number is an adjective before a noun we don’t use an –s.
A two-litres bottle of wine.
- A two-litre bottle of wine.
Don’t forget we add hyphens to multiple word adjectives that go before the noun.
- I have a 500-year-old tree.
(Tree is the noun, 500-year-old is the multiple word adjective that describes it.)
- My ten-year-old daughter.
When the adjective comes after the noun, we use an -s, if it is more than one, but no hyphens.
- A wine bottle which can hold one litre.
(Only one so no -s.)
- My tree is 500 years old.
(More than one so add an -s.)
- My daughter is ten years old.