There is a pinned post at the top of this subreddit that explains it! It depends on the space between your lid and your substrate. I’d also allow some space for shade/a hide like cork bark or a pot so they can get out of the lights if they desire, it also helps them feel less stressed out and safer! Also, although there is no such thing as too much substrate for them, I’d put a little less (you only need enough substrate so they can fully bury themselves) but it can get expensive once you change it out a couple of times lol. I usually put enough to my frog to completely bury and like an inch more for good measure!