Ideally you want the tube to not be so big that it wrinkles or kinks inside the tire/rim. The wrinkles and kinks sometimes can be felt as regular bumps every rotation of the tire and they are points that might be more prone to developing a leak.

Nor do you want it to be so small that it stretches a lot to fill the cavity created by the tire/rim. The more a tube stretches, the more likely it's going to give you quick flats instead of slow flats when something punctures it.

That said there is no standard I know of that says how the mfr's must label their tubes or what dimensions of the tubes must be for what tire. So even if you get a tube that is expressly for a particular size tire. A tube from another manufacturer for that particular size tire might be different.