General word for the property of something that describes how full something is

I’m looking for a general word. A few examples to help illustrate:

• If a class has 10 spots and 4 people have registered, the class’ ____ is 4.
• If you’re filling up a container of unknown capacity and it takes a while and someone asks on your progress, they may inquire about the container’s current ____.
• If a battery or capacitor is 50% charged, its ____ is half.
• If a progress meter or a loading indicator hasn’t progressed very far, its ____ is low.

The closest I’ve come up with is “fullness” (or “level” in the container example, though that’s usually used along with a reference to the thing filling the container, as in “water level” or “the level of the dirt”). But those don’t seem quite right. I think something more generic that could be used in these and other similar cases is what I’m after – any place you have a total and you’re after the current amount filled, whether or not the total or the current amount are specific numbers or general amounts (like nearly empty or nearly full).