Watermelon and Diabetes: Carbs, Glycemic Index and Portions
A cup of watermelon balls has about 12 g of carbohydrate (11 g net). Glycemic index: low to high (50 to 80). Yes, in sensible portions. It tastes sweet but is mostly water, so a cup is modest in carbohydrate.
Watermelon has a high glycemic index in some studies, and that makes people nervous. The reason it still fits is that watermelon is mostly water: a normal serving has a fairly small amount of carbohydrate, which is why its glycemic load is much lower than its index suggests.
The catch is how easily a big wedge becomes several servings. A cup or two at a time, measured out, is easier to fit in than eating straight from the melon.
Carbs in watermelon by portion
| Portion | Grams | Carbs (g) | Fiber (g) | Net carbs (g) | Protein (g) |
|---|---|---|---|---|---|
| cup, balls | 154 | 12 | 0.6 | 11 | 0.9 |
| cup, diced | 152 | 11 | 0.6 | 11 | 0.9 |
| NLEA serving | 280 | 21 | 1.1 | 20 | 1.7 |
| 100 g (for comparing foods) | 100 | 7.5 | 0.4 | 7.1 | 0.6 |
Source: USDA FoodData Central, FDC ID 167765 (Watermelon). Net carbs here means carbohydrate minus fiber. “Net carbs” is not an FDA-defined term, so total carbs are shown too. Values are estimates for a typical item; brands, ripeness and size vary.
Glycemic index and glycemic load
GI ranks how fast a food raises blood glucose compared with pure glucose (100). Low is 55 or less, medium 56 to 69, high 70 or more. The two studies disagree widely, so we show both ends. Glycemic load multiplies the index by the available carbohydrate in a portion (carbs minus fiber), so it reflects how much you actually eat: low is 10 or less, medium 11 to 19, high 20 or more.
Which published values we used (2)
| Entry | Food as listed | GI |
|---|---|---|
| Suppl. Table 2, #3037 | Watermelon (Citrullus vulgaris), raw | 50 |
| Suppl. Table 2, #3039 | Watermelon, raw | 80 |
Atkinson FS et al. International tables of glycemic index and glycemic load values 2021. Am J Clin Nutr 2021;114(5):1625-1632. Glucose reference (glucose = 100); values from studies that used white bread were converted by the authors. Where studies differ we show the range, not an average.
Glycemic index is only one piece of the picture. The same food can give a different response depending on ripeness, cooking, what you eat it with and your own body, so your meter or CGM is the best guide.
How watermelon fit the plate method
Watermelon count toward the carbohydrate quarter of the plate in the plate method, along with grains, starchy vegetables, fruit and milk. The CDC describes the plate method as half non-starchy vegetables, a quarter protein and a quarter carbohydrate foods. See the diabetic meal plan guide for how it works, or drop watermelon onto a meal in the meal planner to watch the plate fill.
Portion ideas and pairings
- One to one and a half cups, cubed.
- Cut it up ahead of time so you eat a portion, not the whole half.
- Serve with feta or a few nuts to round out a snack.
Pairs well with: feta or cottage cheese, a few almonds, plain yogurt.
Related foods
Banana
1 medium: 27 g carbs
Apple
cup, quartered or chopped: 17 g carbs
Strawberries
cup, halves: 12 g carbs
Grapes
cup: 27 g carbs
See all foods and the low glycemic foods list
Frequently asked questions
Is watermelon high glycemic?
It is high on the index in some tests, but its glycemic load per serving is low to moderate because it has little carbohydrate per cup. Portion matters more than the label.
How many carbs are in a cup of watermelon balls?
About 12 g of carbohydrate, of which about 0.6 g is fiber, so roughly 11 g net carbs. Values are from USDA FoodData Central for 154 g and are estimates; brands and sizes vary.
Information only, not medical advice. Your care team may set different targets for you, and only a lab test ordered by a clinician can diagnose diabetes or prediabetes. See our medical disclaimer.
Sources
- USDA FoodData Central: Watermelon (FDC ID 167765)
- Atkinson FS et al. International tables of glycemic index and glycemic load values 2021. Am J Clin Nutr 2021;114(5):1625-1632
- CDC: Diabetes Meal Planning (plate method and carbohydrate counting)
- ADA Standards of Care in Diabetes—2026, Section 5: Facilitating Positive Health Behaviors
Last reviewed: by the Diabetes Blogs editorial team. Information only, not medical advice.
