3"-5" (clearance over the toptube) just to give you a grossly vague idea. the sizing depends on the type of riding you do, your body measurements (inseam and torso), fitting preferences, and other important geometry associated with the bike (brand).

Although its an used bike, you can get the geometry online from the Manufacturer's website.

Please, keep in mind that with the Compack Mountain bike Geometry/design the standover height (in other words, the height of the toptube from the ground) has become a little less significant factor in bike fitting, the Top tube length BB height etc are also very important factor for deciding about the perfect size for you.

Finally, there are some great knowledgable people in this forum who can guide you about that. For some, my suggestion may be totally inappropriate, but I just wanted to give you a ball park idea, or a point to start from.

Please keep in mind, test riding is the best way to find out the right fit. If the bike feels right during test riding, its the right size for you, you can forget all the formulas and opinions.