I put one per short rest, but that's not very accurate.
My players are in Undermountain (old school, not DoMM) so they don't often find healing potions.
When they use healing potions, they tend to use several because its a big fight and they are in trouble etc. But, they only use healing potions maybe once every 10 fights, but then they tend to use all the ones they have.
As GM, you have control over how many healing potions they have access to. Yes, they are i the PHB, but if its a problem with them using too many, then you can simple say they are not available. It's very reasonable that the herbalist in town might only make 1 per week, and the party is not the only one buying them.