According to Wikipedia [1], it's more like 8 glasses (2,5 dl/ 1 cup per glass) of orange juice. That's 2 liters. The apple/grape juice carton I have handy gives a very similiar number. What kind of juice (or portion size) are you thinking of?

[1] https://en.wikipedia.org/wiki/Orange_juice

3 massive glasses - no, I've never drank anything like 2 litres of fruit juice in one day, let along one sitting.