By Dr. Jane Smith · Published April 2, 2025 · 7 min read
How many calories in watermelon? Just 30 calories per 100g — making it one of the lowest-calorie fruits you can eat. A full cup of diced watermelon clocks in at around 46 calories, and a generous wedge (one slice, roughly 1/16 of a melon) contains about 85 calories. The secret is simple: watermelon is 92% water by weight, so most of what you're eating is hydration, not energy.
Calories by Serving Size
The exact number of calories in watermelon depends almost entirely on how much you eat. The USDA FoodData Central lists raw watermelon at 30 kcal per 100g. Here's how that translates to real serving sizes:
| Serving | Approximate Weight | Calories |
|---|---|---|
| Per 100g | 100g | 30 kcal |
| 1 cup diced | 152g | 46 kcal |
| 1 thick wedge (1/16 of melon) | 286g | 86 kcal |
| 2 cups diced | 308g | 93 kcal |
| Whole large watermelon (~10 lbs) | ~4.5 kg | ~1,360 kcal |
Even two full cups — a large, satisfying portion — comes to under 100 calories. That extraordinary calorie-to-volume ratio is what makes watermelon such a smart choice for anyone watching their intake.
Full Nutrition Profile
Calories aside, watermelon delivers a surprising amount of nutritional value per serving. Here is the complete breakdown for 1 cup diced (152g), based on USDA data:
| Nutrient | Amount | % Daily Value |
|---|---|---|
| Calories | 46 kcal | — |
| Carbohydrates | 11.5g | 4% |
| Sugar | 9.4g | — |
| Fiber | 0.6g | 2% |
| Protein | 0.9g | 2% |
| Fat | 0.2g | 0% |
| Vitamin C | 12.3mg | 14% |
| Vitamin A | 865 IU | 17% |
| Potassium | 170mg | 4% |
| Magnesium | 15mg | 4% |
| Lycopene | ~6,890 mcg | — |
ℹ️ The Lycopene Advantage
Watermelon is the richest whole-food source of lycopene, containing roughly 40% more per 100g than raw tomatoes. Lycopene is a powerful antioxidant linked to reduced cardiovascular risk and lower rates of certain cancers, according to a review published in the Asia Pacific Journal of Clinical Nutrition.
Watermelon also contains citrulline, an amino acid that the body converts to arginine — which helps dilate blood vessels and may improve blood flow and exercise recovery.
Glycemic Index: High Number, Low Real-World Impact
Watermelon's glycemic index (GI) of around 72 often surprises people — that number is technically in the "high" range. But GI alone is a poor predictor of how a food actually affects your blood sugar.
What matters more is glycemic load (GL), which accounts for how much carbohydrate is actually in a serving. A 1-cup portion of watermelon has only 11.5g of net carbs. Plug those numbers in and the GL comes out at just 4–8 — firmly low.
The reason is that 92% of watermelon's weight is water. You'd have to eat an enormous amount to deliver the same carb load as a slice of bread. For most people, a standard serving has a moderate effect on blood sugar, particularly when eaten alongside protein or fat.
Research suggests that pairing watermelon with a small amount of nuts, cheese, or yogurt further slows glucose absorption and stabilizes blood sugar response.
Is Watermelon Good for Weight Loss?
Yes — and there's clinical evidence to support it. A 2019 study gave overweight adults either watermelon or low-fat cookies daily for four weeks. The watermelon group experienced greater satiety, reduced body weight, lower BMI, smaller waist circumference, and improved blood pressure. The cookies group saw none of these benefits.
Three properties drive watermelon's diet-friendly profile:
- Extreme volume-to-calorie ratio — 92% water means you eat a large, filling portion for very few calories.
- High water content supports hydration — staying hydrated is consistently linked to better appetite regulation.
- Satisfying sweetness — the natural sugar in watermelon can satisfy a sweet craving for far fewer calories than processed desserts.
For a broader look at how fruit fits into a calorie-conscious diet, see our guide on calories and weight loss.
Watermelon vs. Other Summer Fruits
How does watermelon compare calorie-for-calorie to other popular fruits?
| Fruit (per 100g) | Calories | Carbs | Sugar | Water % |
|---|---|---|---|---|
| Watermelon | 30 kcal | 7.6g | 6.2g | 92% |
| Strawberries | 32 kcal | 7.7g | 4.9g | 91% |
| Cantaloupe | 34 kcal | 8.2g | 7.9g | 90% |
| Peach | 39 kcal | 9.5g | 8.4g | 89% |
| Apple | 52 kcal | 13.8g | 10.4g | 86% |
| Mango | 60 kcal | 15g | 13.7g | 83% |
| Banana | 89 kcal | 22.8g | 12.2g | 75% |
| Grapes | 69 kcal | 18g | 15.5g | 81% |
Watermelon and strawberries are virtually tied as the lowest-calorie fruits by weight — both hover around 30–32 kcal per 100g. The key difference is that watermelon's larger serving size makes it more volumetrically satisfying.
For a deeper comparison between different fruit options, see our article on how many calories are in an apple.
Hydration Bonus
A 2-cup serving of watermelon delivers roughly 280ml of water — nearly a full glass. Since the body absorbs water from food alongside electrolytes like potassium and magnesium, watermelon may hydrate more efficiently than plain water alone.
Diet Quality: What the Research Shows
A large analysis of 56,133 U.S. adults and children from the NHANES dataset (published in Nutrients, 2022) found that regular watermelon consumers scored 6.6–7.3 points higher on the Healthy Eating Index compared to non-consumers. They also had:
- Higher intake of fiber, magnesium, potassium, and vitamin A
- Lower intake of added sugar and saturated fat
- Significantly higher lycopene levels — over 10,000 mcg more per day
The takeaway: watermelon isn't just a low-calorie treat. People who eat it regularly tend to have better overall diets. Understanding your complete nutrition picture goes beyond any single food — our guide on what a balanced diet actually means explains the full framework.
Frequently Asked Questions
How many calories are in a cup of watermelon?
One cup of diced watermelon (about 152g) contains 46 calories, 11.5g of carbs, 9.4g of sugar, 0.6g of fiber, and 0.9g of protein. Nearly all of the weight is water — making it one of the most hydrating and lowest-calorie snacks available.
Is watermelon good for weight loss?
Research says yes. Clinical studies show that daily watermelon consumption reduces body weight, BMI, and waist circumference more than equivalent-calorie snacks. Its high water content, natural sweetness, and very low calorie density make it easy to eat a satisfying portion without overshooting your daily intake.
Does watermelon raise blood sugar?
Watermelon has a high glycemic index (GI ~72), but its glycemic load per serving is low (4–8) because each serving contains very few net carbs. Most people can enjoy a 1-cup portion without a significant blood sugar spike. Pairing it with protein or a small amount of fat further smooths the glucose response.
How many carbs are in watermelon?
Watermelon contains 7.6g of total carbs per 100g, with 6.2g as sugar and only 0.4g as fiber. A 1-cup serving has about 11.5g of total carbs. These are naturally occurring sugars — no added sugar, no refined carbohydrates.
Is watermelon high in sugar?
Compared to many fruits, watermelon has a moderate sugar content (6.2g per 100g). Because the fruit is 92% water, you eat a large volume for relatively little sugar. A full cup has about 9.4g of natural sugar — less than a medium apple and far less than a glass of orange juice.
Start Tracking What You Eat
Watermelon is one of the most diet-friendly foods you can reach for — but knowing how it fits into your full day is what drives real results. Caloria makes it effortless: snap a photo of your meal and get an instant calorie and macro breakdown with no manual entry.
⚠️ Medical Disclaimer
This article is for informational purposes only and does not constitute medical advice. If you have diabetes or a condition that requires blood sugar management, consult a registered dietitian or healthcare professional before making significant dietary changes.