This forum will focus on the interesting topic of titrating oral vitamin C intake to so-called bowel tolerance, the point just prior to the onset of diarrhea
Oranges come in quite a range of sizes and are picked in varying states of ripeness and are often stored in less than perfect conditions. A range of 50 to 80 milligrams would probably cover most of the fruit you are likely to find.
Do the math!
If 180 gms of orange contain 95.8 mg of Vit C.
Then, for example, 135 gm of orange would contain 71.85 mg of Vit C.
Or, 225 gm of orange would contain 119.75 mg.
Cups should work the same way. 3/4ths of a cup should also contain 71.85 mg.