If you want to use fresh grapefruit juice in a recipe or making, or you just need to know how much grapefruit you need to serve fresh-squeezed grapefruit juice for breakfast or an event, it can be kind of hard to just how much juice as single grapefruit can make.
One medium or average-sized grapefruit will make about 3/4 cup of fresh-squeezed grapefruit juice. Some of the exceptionally large variety of grapefruit you can sometimes find in the grocery store will produce a bit more grapefruit juice, about 1 cup.
When picking your grapefruit for making grapefruit juice, pick ones that have firm skin and feel heavier than others. Older grapefruit will tend to dry out over time and feel lighter, especially since you don’t know how much time has passed since the fruit was on the tree versus when you buy it at the store.