As previously mentioned, one straddled the bike standing straight up. The general rule of thumb was you wanted 1-2 inches of top tube clearance in case you came off the saddle, you didn't land on the family jewels. Thinking was much different 20-30 years ago. Case in point--I have a 36 inch inseam and ride a 25 inch frame (the tallest Peugeot made). I bought that bike new 35 years ago. It's my one and only bike and it still fits and is comfortable to ride all day long.
Jon