Possessive ’s with time expressions – Two hours’ walk

The use of the possessive ’s with time expressions

We don’t normally use the possessive ‘s with inanimate things. In those cases, we generally use of instead. For example, we say:

• the end of the street (NOT the street’s end)
• the first page of the document (NOT the document’s first page)

However, the possessive ’s is often used in time expressions to talk about the duration of something. For example:

• You need two years’ experience to get a job.
• He lives one hour’s drive from the airport.
• The three hours’ journey to the valley was amazing.

Note that the apostrophe is sometimes not included, but this is usually not considered correct.
 

When do we need to use the possessive ’s with time expressions?

If you are not sure whether you should use the possessive ’s with a time expression, you can try replacing it with the word of. If the expression still makes sense, it means that you should use the ’ (apostrophe) or ’s.

For example, we say:

• two years’ experience (=an experience of two years)
• one hour’s drive (=a drive of one hour)
• three hours’ journey (=a journey of three hours)

But we say:

• It’s two months old. (The expression two months of old does not make sense.)
• She is nine months pregnant. (The expression nine months of pregnant does not make sense.)

The possessive ’s with singular and plural time expressions

The form of the possessive ’s with time expressions is the same as with other nouns.

• Add ’s after singular nouns: one year’s notice, an hour’s walk, etc.
• Add only ’ (apostrophe) after plural nouns ending in -s: three years’ notice, two hours’ walk, etc.

A two-day journey = two days’ journey

We also often use number + time expression before nouns to talk about how long something lasts.  In this case, the number and the time expression are joined by a hyphen and the time word is singular.

• a four-hour journey = four hours’ journey
• a thirty-minute delay = thirty minutes’ delay
• a two-hour drive = two hours’ drive

Note that this type of number + noun compound adjective is also used to talk about other kinds of measurements.

• a one-hundred-dollar bill
• a five-litre bottle
• a twenty-foot container