Coolant overflow capacity?

Mine's "just" a thick walled, translucent, graduated 48 oz "water cup", with the overflow tube right through the lid, down to about 1/8" from the bottom.

Works very well.

I glance at it every 3rd or 4th time I drive and if it's lower than about 1/4 full, I add a little.

When it was 16 or 24 oz, I had to add almost every time.

Now I don't.

OK, now that I'm thinking, I might need to check my actual oz capacity.
I just remember that it was too small, and when I increased it, the issues got resolved.