{days / days'} worth of stuff?

Question

I'm confused. When reading a novel, I've encountered

It's around 3 days worth of stuff.

I thought "why not 3 days' worth of stuff?"

So I checked the Sketchengine, and got 2.2k results for "days worth of" and 1.2k for "days' worth of".
In both cases, there were constructs such as "number days worth of noun".

As I understand, the first version is a noun string, when the second one basically says "this amount of work [belongs to / is done within] three days", so my guess is that both forms can be used, but the first one without the apostrophe is more reasonable.

Could you please verify my thoughts?

Answer 1

This should be written with a possessive. Consider the case "It's around one day's worth of stuff". That is clearly correct and the singular possessive can be used. "One day worth" would be wrong. Therefore in the plural case, the plural possessive should be used:

Three days' worth.

However, this is one of those punctuation rules that are very often broken and "Three days worth" is very common. A professional novelist with a good editor should fix that kind of glitch, but it is so common that they might let it pass or just not notice it.

There is potential for confusion with "day" used as a unit in an adjectival phrase, for which the singular is used

We went on a three-day hike.