A typical fresh watermelon is very low in calories: roughly 30 calories per 100 g, about 46 calories per cup of diced watermelon, around 86 calories in a large wedge (about 1/16 of a melon), and about 1,360 calories in an entire large watermelon.

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How Many Calories in a Watermelon?

If you’ve ever demolished half a watermelon in one sitting and then thought, “Did I just eat my whole day’s calories?”, the reassuring news is: probably not.

Quick Scoop

  • About 30 calories per 100 g of watermelon.
  • Around 46 calories in 1 cup of diced watermelon.
  • About 86 calories in 1 big slice (1/16 of a standard melon).
  • A whole large watermelon (about 15 in long, 7.5 in diameter) has roughly 1,360 calories.

So yes, it’s sweet and refreshing, but still surprisingly light on energy.

How Many Calories in Common Portions?

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Portion Approx. Calories Notes
100 g watermelon ~30 kcal Standard reference value.
1 cup, diced ~46 kcal Great for quick tracking apps.
1 large slice (1/16 melon) ~86 kcal Classic BBQ wedge.
Half a watermelon ~450–650 kcal (typical) Depends on size; based on ~30 kcal/100 g.
Whole large watermelon ~1,360 kcal USDA estimate for a ~15-inch melon.
Because watermelon is mostly water (around 90%+), its calorie density stays **low** compared with its volume.

Why the Numbers Vary

Not every melon is identical. A few things shift the exact calorie count:

  • Size and weight
    Larger watermelons obviously pack more total calories, even though calories per 100 g stay about the same.
  • Variety (seeded, seedless, yellow)
    Most common types sit around the same ballpark of ~30 calories per 100 g; sweetness may vary a bit, but the difference in calories is small.
  • How much you actually eat
    We don’t eat the rind, and personal‑size melons can range from ~3 to 7 lb, so the actual calories you consume will depend on edible weight.

Think of the 30 kcal/100 g number as your baseline ; everything else is just a multiplication problem.

Watermelon and Weight Loss: Friend or Foe?

From a calorie perspective, watermelon leans heavily toward “friend.”

  • Low energy density : Lots of water, modest sugar, very few calories per bite.
  • High volume : It fills your stomach, which can help with satiety if you’re used to eating large portions.
  • Micronutrients : It provides vitamins A and B9, plus plant compounds like lycopene and citrulline.

The catch: it’s easy to underestimate how much you’ve eaten. Half a medium melon can still land you around 450–650 calories, which is significant if your daily target is tight.

A simple approach:

  1. Decide how many calories you want to “spend” on snacks.
  2. Use 30 kcal per 100 g as your rough guide.
  3. Cut a portion you can track (e.g., fill a 1–2 cup container).

What People in Forums Say

You’ll see a range of numbers in forum discussions, but they generally orbit the same truth: watermelon is low calorie per gram, but a whole one can still add up.

“Watermelon is 30 kcal per 100 g… personal watermelons can range from 3–7 lbs, so roughly 408–953 kcal.”

“An entire watermelon is only 800 cal.” (A common claim in diet forums—real number varies with size.)

Some posts even claim a large watermelon is around 1,000 calories, which aligns fairly well with the ~1,360 kcal USDA estimate for a big specimen.

The takeaway from these conversations:

  • Per bite, it’s light.
  • Per whole fruit, it’s still food you should count.

Mini How‑To: Estimating Your Own Slice

If you want a quick, “good enough” number:

  1. Weigh the edible part (if possible).
    • Example: Your bowl of cubed watermelon weighs 300 g → 3 × 30 = ~90 calories.
  1. No scale? Use cups.
    • 1 cup diced ≈ 46 calories; 2 cups ≈ ~90 calories, 3 cups ≈ ~135 calories.
  1. Big BBQ wedge?
    • If it looks like a standard 1/16 slice from a classic big melon, count ~86 calories.

It doesn’t have to be perfect; for most people, staying in the right range is what matters.

Is Watermelon “Too Sugary”?

Watermelon does taste very sweet, so it often gets labeled as “sugar bomb,” but its sugar is diluted in a lot of water.

  • About 6.2 g of sugar per 100 g, with only ~30 calories.
  • That’s fewer calories per 100 g than bananas, grapes, or mangoes.

For most healthy people, watermelon fits comfortably in a balanced diet, especially if you pair it with protein or healthy fats (like a handful of nuts or some Greek yogurt) to smooth out blood sugar impact.

TL;DR (Bottom Summary)

  • Per 100 g : ~30 calories.
  • Per cup (diced) : ~46 calories.
  • Per big slice : ~86 calories.
  • Whole large watermelon : ~1,360 calories.

Watermelon is low in calories for its size, rich in water and helpful nutrients, and can be an easygoing part of weight loss or maintenance as long as you remember that “half a melon” is still a real chunk of your daily intake.

Information gathered from public forums or data available on the internet and portrayed here.