There are 74 calories in a pink grapefruit measuring 3 and 3/4". A standard serving of half a grapefruit contains approximately 37 calories. Canned grapefruit is higher in calories and sugar.
Fresh grapefruits are low in calories and have no fat. They also contain fiber, vitamin C and vitamin A. Grapefruits have high levels of antioxidants, such as lycopene, a carotenoid that gives the fruit its distinctive pink color. Though full of vitamins and minerals, grapefruit is known to interact with some medications and can cause serious side effects. Talk to a doctor if there are concerns about how a medication reacts to grapefruit.