Start with the septic tank size guide for the tables and how states differ. For a typical home, the 3-bedroom page gives the short answer, and how big a drain field needs to be covers the part that takes over the yard.
Before anything is installed, the lot has to pass a perc test, and the result decides which system it can take. Already own a system? See how deep tanks usually sit and how to find a buried tank, cheapest method first. If you are planning something small, read septic options for a tiny house, cabin or ADU.
Minimum sizes come from state and county codes, and they change. Check the current rule with your local health department before you design or buy.
