You need to find out the exact engine type installed (e.g. O-320-XXXXX) and get the manual for the engine, which will specify the minimum oil level.
There will also be a maximum level but as Whopity says, usually filling it to max just causes the engine to blow out the extra out of the breather. For example mine is 6qts min and 12qts max, but anything over 10 is quickly lost, so I run it between 8 and 9.
The engine manual will also specify maximum oil consumption. If it is worse than this then the engine is not airworthy so the aircraft cannot be flown. However this figure is scarily high - of the order of 1qt to 2qt per hour
If you are burning anywhere near that figure then I suggest you stick to nice flat countryside and do the national lottery regularly
What is it actually burning? 0.1qt/hr is about right for a good engine, 0.3qt/hr for a somewhat shagged one, and those figures are for the 6-cyl IO540-C4. Yours should be less.