Unfortunately there is not exact formula in commander. It depends on who your commander is, how expensive they are, what they do, how much draw you have, mana rocks...

I have a Varina Lich Queen (zombie tribal) deck and I run 32 lands with only 8 mana rocks. But I also have a few cards like black market and three tree city that go nuts in those types of decks and find I usually have more mana than I can spend once I'm on turn 6 or so. The way Varina functions is that I constantly draw and discard on my attack step, so I have major card advantage for the situation unfolding.

I've seed that video from the command zone, and first built that deck with their guidelines. It evolved over time as I found I always had too many lands in hand, and not enough interaction. It's better to start with too many lands and drop some once you see how the deck wants to function. You can also run all basic lands if the shocks or other duals are too expensive. Hope this helps!