I'm trying to choose a ring size for a binder to carry between my desk and meetings, mostly for current notes and a few reference sheets. Smaller rings keep the whole thing less bulky, but leave less room as pages build up; larger rings are easier to flip through, though they start to feel like more binder than I need. I can't decide which trade-off matters more for something that's meant to stay portable.
For carrying it between desk and meetings, I'd go with the smaller rings. Move finished notes out as it fills up instead of carrying extra bulk for pages you might not need.
Count the reference sheets, dividers and any pockets first. They stay put when finished notes come out, so they set the minimum ring capacity.