Watermelon has a high glycemic index, around 80, but a low glycemic load of about 5 for a typical serving. That combination sounds contradictory, but it isn't: watermelon is mostly water, so a normal cup of cubes carries very little actual carbohydrate, and the real-world impact on blood sugar is mild despite the high index number.
The numbers
Harvard Health cites watermelon at a glycemic index of about 80 and a glycemic load of just 5 for a typical serving, the same figures already used elsewhere on this site. A one-cup serving of cubes has only about 11 grams of carbohydrate, because watermelon is roughly 92 percent water.
| Food | GI | Typical serving carbs | Glycemic load |
|---|---|---|---|
| Watermelon (1 cup cubes) | ~80 (high) | ~11g | ~5 (low) |
| White rice (½ cup cooked) | ~73 (high) | ~22g | ~16 (medium) |
80 × 11 ÷ 100 ≈ 9, close to Harvard's cited figure of 5 once you account for slightly different portion assumptions. Either way, it lands solidly in the low range.
Why the GI number alone is misleading here
Glycemic index measures how fast a food's carbohydrate raises blood sugar, compared gram for gram with pure glucose. It says nothing about how much carbohydrate is actually in a real serving. Watermelon is the textbook example: its carbs act fast, but there simply aren't many of them in a normal portion, so the real effect is mild. If you judged watermelon by its index number alone, you'd avoid it for no reason. We go deeper into this exact distinction, using watermelon as the lead example, in our full glycemic index vs. glycemic load guide.
A cup or two of watermelon is a genuinely low-glycemic-load treat on its own. The load adds up the way any food's does if you eat several servings in one sitting or pair it with other high-carb foods at the same meal, so it's the total plate that matters, not watermelon in isolation. For another fruit where ripeness changes the picture a lot, see our bananas page.
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