How many calories are in grapefruit?
Grapefruit has 52 calories per 1/2 medium (123 g) — that's 42 calories per 100 g, roughly 3% of a 2,000-calorie day. Most of those calories come from carbohydrate.
USDA FoodData Central · raw · FDC 174673
Calories by portion
| Portion | Calories | Protein | Carbs | Fat |
|---|---|---|---|---|
| 1/2 medium (123 g) | 52 | 1 g | 13.2 g | 0.1 g |
| 100 g | 42 | 0.8 g | 10.7 g | 0.1 g |
| 1 oz (28 g) | 12 | 0.2 g | 3 g | 0 g |
Where the calories come from
Protein 7% Carbs 91% Fat 2%
Calories computed from USDA per-100 g data (FDC 174673, SR Legacy). raw. The macro split uses general Atwater factors (protein and carbs ≈ 4 cal/g, fat ≈ 9 cal/g) and is approximate.
Half a medium grapefruit carries about 52 calories — straight from USDA’s 42 calories per 100 g for a 123 g half. Nearly all of that energy is carbohydrate, mostly natural sugar, wrapped in a fruit that is otherwise mostly water. This is the food that launched a thousand diets, and the calorie math explains why: grapefruit is genuinely low-energy, refreshing, and filling, so half a grapefruit to start the day or a meal costs you almost nothing while feeling like a real serving of fruit.
Where the calories in grapefruit come from
Grapefruit is a carbohydrate food in the lightest possible sense. Of those ~52 calories, roughly 91% come from carbohydrate — natural sugar plus a little fiber — with about 7% from its small protein content and barely 2% from fat. There is essentially nothing else in the mix, and the absolute total is so small that grapefruit barely registers on a daily count. The standout is what comes alongside those few carbs: half a grapefruit covers a large share of the day’s vitamin C, and the pink and red varieties add the antioxidant lycopene.
One of the lowest-calorie fruits you can eat
On calorie density, grapefruit sits near the bottom of the fruit pack — even lighter than berries — because it is so heavily water and fiber. That is the entire logic behind eating it for weight management: a big, juicy half-fruit adds volume and fullness to a meal for about 52 calories, so it helps you feel satisfied while keeping the total down. There is no fat-burning trick here, just a smart, filling, low-energy food. The one practical caution worth flagging has nothing to do with calories: grapefruit can interact with several common medications, so check with a pharmacist if you take prescription drugs.
For the flip side of the macro picture, see protein in grapefruit — and treat grapefruit’s calories as the honest, low number they are.
Frequently Asked Questions
How many calories are in half a grapefruit?
About 52 calories in half a medium grapefruit (123 g), based on USDA's 42 calories per 100 g (FDC 174673). A whole grapefruit runs around 103 calories. That low number is exactly why grapefruit earned its reputation as the classic 'diet' fruit.
How many calories are in grapefruit per 100 g or per ounce?
42 calories per 100 g, which is about 12 calories per ounce (28 g). That is a very low calorie density — grapefruit is mostly water and fiber, so you get a refreshing, filling fruit for almost no energy cost.
Where do the calories in grapefruit come from?
Almost entirely carbohydrate. Using standard Atwater factors, roughly 91% of grapefruit's calories come from carbs — natural sugar and a little fiber — with about 7% from its ~0.8 g of protein per 100 g and only ~2% from its trace of fat. Grapefruit is essentially water, vitamin C, and a small amount of carbohydrate.
Is grapefruit good for weight loss?
It is close to ideal as a low-calorie fruit. At about 52 calories a half with fiber and a lot of water, grapefruit adds volume and a feeling of fullness to a meal for very little energy — which is the real reason behind the old 'grapefruit diet' idea. There is nothing magic about grapefruit burning fat, but starting a meal with one is a genuinely sensible, filling, low-calorie habit.
How many calories are in a whole grapefruit?
About 103 calories for a whole medium grapefruit (around 246 g), since the half-fruit serving is roughly 52 calories. Even the full fruit stays close to 100 calories — a substantial, refreshing portion for the energy of a small snack.
When was this data last verified?
2026-06-04, against USDA FoodData Central FDC 174673 (Grapefruit, raw, pink and red, all areas; SR Legacy). We re-verify reference pages periodically and update when the underlying USDA entry changes.
Whole-food values are USDA reference data, not a Labelgrade (that score is for branded packaged products). See our methodology and the TDEE calculator to turn this into a daily target.