Calculating Bankroll for Home Games and Local Tournaments

I am quite new in poker and trying to understand how to manage my bankroll properly for small local games and occasional home tournaments. Many players talk about risk and proper buy-in, but I am still confused about how much to keep aside to feel safe while still playing comfortably. In my day work, I sometimes deal with residential estimates for small construction projects, so I am used to calculating costs carefully. I think this habit helps me a bit with thinking about how much money to allocate per session, but poker feels more unpredictable than a normal project. I am curious how other players manage this do you set strict limits for each session or keep a flexible amount depending on the stakes? Any advice from regular home game players would be really helpful.