Watermelon Nutrition Facts: How Many Calories Does Watermelon Have?

Watermelon provides about 46 calories in a 1-cup diced serving (152 g / 5.4 oz) and 30 calories per 100 g (3.5 oz). The fruit is roughly nine-tenths water by weight, which is why a big-looking bowl still lands under 50 calories. Every number on this page comes from the USDA FoodData Central panel for raw watermelon (FDC ID 167765), with per-cup values scaled from that same panel.

🔥 How Many Calories Does Watermelon Have?

Watermelon has 30 calories per 100 g (3.5 oz) and about 46 calories per 1-cup diced portion (152 g / 5.4 oz). Virtually all of those calories come from carbohydrate (7.55 g per 100 g), while fat (0.15 g) and protein (0.61 g) are close to zero. Because the fruit is mostly water, calories scale almost directly with the size of your slice.

Typical portions:

• 100 g (3.5 oz): 30 calories
• 1 cup diced (152 g / 5.4 oz): about 46 calories
• 1 wedge cut from a 10-lb (4.5 kg) melon — roughly 1/16 of the fruit, about 280 g / 9.9 oz: about 85 calories
• 1 whole small melon (5 lb / 2.3 kg): about 680 calories

Key takeaway: At 30 calories per 100 g, watermelon is one of the lowest-calorie fruits you can eat — a 1-cup portion costs less than a single tablespoon of most nut butters.

📊 Watermelon Nutrition Facts Per 100 g and Per Cup

The per-100 g column is the USDA value as published; the per-cup column multiplies it by 1.52, the gram weight of a standard 1-cup diced portion. Net carbs — total carbohydrate minus fiber — work out to about 7.15 g per 100 g and about 10.9 g per cup. Watermelon is a low-fiber fruit, so most of its carbohydrate arrives as sugar rather than starch or fiber.

🍉 Hydration: A Water-Rich Fruit

Watermelon is roughly 91% water by weight, so a 1-cup diced portion (152 g) delivers about 140 mL (4.7 fl oz) of fluid along with a small amount of electrolytes. That fluid counts toward daily hydration, the same way water from other foods and drinks does.

• Potassium: 112 mg per 100 g (2% DV) — the main electrolyte watermelon contributes
• Fluid: about 140 mL (4.7 fl oz) per 1-cup portion
• Practical note: watermelon is a pleasant way to add fluid on a hot day, but it does not replace drinking water during prolonged heat or exercise.

Because the sugar content is modest per 100 g, hydration is the more meaningful nutrition story here than micronutrient density. If you are tracking fluid rather than calories, log the gram weight and convert using the water content.

🍞 Sugar Content and Glycemic Index

Watermelon carries 6.2 g of sugar per 100 g — about 9.4 g in a 1-cup portion. That sugar is naturally occurring rather than added, and whole fruit is excluded from the "free sugars" that the World Health Organization recommends keeping under 10% of daily calories.

Watermelon's glycemic index is 72, which falls in the high range (70 or above). Glycemic index alone is misleading here, because watermelon contains very little carbohydrate per gram. Glycemic load — glycemic index multiplied by available carbohydrate (total carbohydrate minus fiber) — is about 5.1 per 100 g (72 × 7.15 g ÷ 100) and about 7.8 per 1-cup portion (72 × 10.9 g ÷ 100), both in the low range.

• GI 72: high
• GL per 100 g ≈ 5.1: low
• GL per 1-cup portion ≈ 7.8: low

Measured GI for watermelon varies with variety, ripeness, and study method, so treat 72 as a reference point rather than a fixed property of every melon.

💊 Vitamins, Minerals, and Plant Compounds

Per 100 g, watermelon supplies vitamin C and vitamin A, plus a modest amount of potassium. It is not a multivitamin in fruit form — the amounts are real but small — and its most distinctive contribution is water volume rather than micronutrient density.

• Vitamin C: 8.1 mg per 100 g (9% DV)
• Vitamin A: 28 mcg RAE per 100 g (3% DV)
• Potassium: 112 mg per 100 g (2% DV)

Watermelon is also one of the richest common food sources of lycopene, the carotenoid usually associated with tomatoes, and it contains citrulline, an amino acid studied for vascular and exercise-related effects. These are areas of active research, so the practical takeaway is a fruit that hydrates well and adds a small amount of antioxidant compounds — not a therapeutic dose of anything.

⚖️ Weight Loss, Keto, and Diabetes Considerations

Watermelon sits in an unusual spot: very low in calories per gram, yet relatively high in fast-digesting sugar per serving. Whether it helps or hinders depends almost entirely on portion size and what you eat alongside it.

• Weight loss: flagged as not friendly in Victura's system. At 30 kcal per 100 g it is not calorie-dense, but it is easy to eat 3–4 cups at one sitting, and the sugar arrives without much fiber or fat to slow it down.
• Keto: not keto friendly. At roughly 7.15 g net carbs per 100 g — about 10.9 g per cup — watermelon uses a large share of a standard 20–30 g daily carb budget.
• Diabetes: flagged as not friendly, with a glycemic index of 72 and 6.2 g sugar per 100 g. A 1-cup portion still has a low glycemic load, so pairing it with protein or fat and keeping the portion small is the usual practical strategy.

These flags are general guidance, not medical advice. Anyone managing blood glucose, following a therapeutic diet, or taking medication should confirm portions with a clinician or registered dietitian.