How many calories are in watermelon?
A cup of diced watermelon, about 150 g, is roughly 45 kcal, and the flesh is about 30 kcal per 100 g. A generous bowl is 75 kcal and a restaurant wedge around 85. Watermelon’s reputation as a fruit to avoid comes entirely from its glycaemic index, which measures something other than energy.
Per portion
| Portion | Calories | Protein | Carbs | Fat |
|---|---|---|---|---|
| 100 g flesh | ~30 kcal | 0.6 g | 7.6 g | 0.2 g |
| 1 cup diced (~150 g) | ~45 kcal | 0.9 g | 11 g | 0.2 g |
| 1 bowl (~250 g) | ~75 kcal | 1.5 g | 19 g | 0.4 g |
| 1 wedge, a sixteenth of a melon (~285 g flesh) | ~85 kcal | 1.7 g | 22 g | 0.4 g |
| 500 g flesh (a hot-afternoon quantity) | ~150 kcal | 3 g | 38 g | 0.8 g |
| 250 ml watermelon juice | ~70–90 kcal | 1 g | 19 g | 0.2 g |
What changes the number
Sweetness, a little. Melons run roughly 8 to 12 per cent sugar by weight depending on variety and ripening, which moves the flesh between about 28 and 36 kcal per 100 g. Seedless, seeded and yellow-fleshed are all in that band.
Rind, a lot — but only if you weigh wrong. Flesh is about two-thirds of a whole melon, and every figure above refers to flesh. The same trap bites harder with muskmelon.
Juicing. Blending 400 g of flesh gives you about 120 kcal you can drink in thirty seconds, chewing and bulk removed, sugar intact — the one preparation that makes watermelon worse value.
What goes on it. Salt, chilli and chaat masala are free. Feta and olive oil are not — 25 g of feta and a teaspoon of oil add about 110 kcal to a salad that started at 60. A cooler built on sugar syrup runs 150 to 250 kcal a glass.
Where it fits in a deficit
At 91 per cent water it sits on the bottom rung of the density ladder: 250 g of food for 75 kcal. As a dessert substitute it is unusually good value — that bowl against two scoops of ice cream at 250 to 300 kcal is a swap you barely notice making.
Where it is weak is holding you. There is almost no fibre (about 0.4 g per 100 g), no fat and under 2 g of protein in a large bowl, so fullness is water-based and short-lived: watermelon is the sweet end of a meal, not the thing that gets you to dinner.
High glycaemic index does not mean high calorie
Watermelon’s GI is somewhere around 70 to 80, up near white bread, and that single number is the whole basis of “watermelon makes you fat”. Two different measurements are being confused.
Glycaemic index ranks how fast the carbohydrate in a fixed 50 g dose of carbohydrate raises blood glucose. To get 50 g of carbohydrate out of watermelon you need about 650 g of flesh — most of a small melon. The glycaemic load of a normal 150 g portion is roughly 4, among the lowest of any fruit, because there is so little carbohydrate there to be fast about.
Calorie density is a different measure: kilocalories per 100 g. Watermelon is low on it for precisely the reason its GI is high — the little carbohydrate it holds is simple sugar dissolved in a great deal of water, and water carries no energy. Dilution lowers the density without lowering the GI. Cucumber does the same one rung further down: at 15 kcal per 100 g it is effectively free.
If you are managing blood glucose, GI is worth knowing. If you are managing weight, the only figure that enters the arithmetic of a calorie deficit is kilocalories per portion.
Figures are typical values and vary by variety, size and preparation. General information, not medical advice.