A medium ripe banana (about 118 grams with the peel) contains roughly 27 to 28 grams of carbohydrates. Of those, about 15 grams come from sugar and 3 grams from fiber, with the remainder as starch. That single banana also delivers around 110 calories, with carbs accounting for nearly all of them.
Carbs by Banana Size
Banana size varies more than most people realize, and the carb count shifts accordingly. The USDA bases its standard serving on a medium banana weighing 118 grams (about 4.5 ounces with the peel). Because carbohydrate content scales almost linearly with weight, you can estimate for other sizes:
- Extra-small (about 4 inches, 81g): ~19 grams of carbs
- Small (about 6 inches, 101g): ~23 grams of carbs
- Medium (about 7 inches, 118g): ~27 grams of carbs
- Large (about 8 inches, 136g): ~31 grams of carbs
- Extra-large (9+ inches, 152g): ~35 grams of carbs
If you’re counting carbs closely, weighing the banana without the peel gives you the most accurate number. The peel accounts for roughly 30 to 40 percent of the total weight.
How Ripeness Changes the Carb Makeup
The total grams of carbohydrates in a banana stay roughly the same whether it’s green or covered in brown spots. What changes is the type of carb inside. A green banana is packed with starch, while a fully ripe banana has converted almost all of that starch into sugar. By the time a banana is ripe with yellow skin, it contains only about 1% starch. Once it’s overripe (heavily spotted or browning), the starch drops to essentially zero.
In a fully ripe banana, total sugars make up about 23% of the fruit’s weight. Sucrose accounts for more than 70% of those sugars, with glucose and fructose splitting the rest roughly evenly. As the banana moves past ripe into overripe territory, sucrose breaks down further, and the glucose-to-fructose share increases. This is why very ripe bananas taste noticeably sweeter even though the total carb count hasn’t really budged.
This matters practically. If you eat a green banana, you’re getting more resistant starch, a type of fiber your body can’t fully digest. One study found that the least ripe bananas contained about 18% resistant starch, while the most ripe ones had dropped to just 2.7%. That resistant starch feeds beneficial gut bacteria and produces a slower, gentler rise in blood sugar. In a ripe banana, the simple sugars hit your bloodstream faster.
Glycemic Index: Green vs. Ripe
The shift from starch to sugar has a measurable effect on blood sugar response. Green, unripe bananas have a glycemic index (GI) of about 30, which puts them in the low category alongside foods like lentils and most vegetables. A well-ripened banana scores around 60, placing it in the medium GI range. For context, pure glucose sits at 100.
A GI of 60 means a ripe banana raises blood sugar moderately, not as fast as white bread but faster than an apple or a handful of berries. The 3 grams of fiber in each banana help slow absorption somewhat, but a ripe banana will still produce a quicker spike than its green counterpart.
Carb Counting for Blood Sugar Management
If you’re tracking carbohydrates for diabetes or another blood sugar condition, bananas require some attention to portion size. The CDC defines one “carbohydrate choice” as 15 grams of carbs. By that standard, one extra-small banana (about 4 inches long) equals a single carb choice. A medium banana counts as closer to two carb choices, which can use up a significant portion of a meal’s carb budget if you’re aiming for 30 to 45 grams per meal.
Pairing a banana with protein or fat (peanut butter, yogurt, a handful of nuts) slows digestion and blunts the blood sugar spike. Choosing a slightly less ripe banana, one that’s yellow but still firm with no brown spots, also gives you more resistant starch and a lower glycemic response.
What Else Is in Those 110 Calories
Nearly all the calories in a banana come from carbohydrates. There’s virtually no fat and only about 1 gram of protein. But bananas carry a solid micronutrient profile alongside those carbs. A medium banana provides around 450 milligrams of potassium, which is about 10% of the daily recommended intake for most adults. Potassium supports normal blood pressure, muscle function, and fluid balance. Bananas are also a good source of vitamin B6, which your body uses to metabolize protein and produce neurotransmitters.
The 3 grams of fiber per banana is modest compared to foods like beans or raspberries, but it still contributes meaningfully to the 25 to 30 grams most adults should aim for daily. In a less ripe banana, you also get the bonus of resistant starch on top of that fiber count, since resistant starch isn’t captured in the standard fiber measurement on nutrition labels.