A medium banana has about 105 calories. That’s based on a banana weighing roughly 118 grams (about 7 to 8 inches long), which is the standard size you’ll find in most grocery stores. Of course, bananas vary quite a bit in size, and the calorie count scales accordingly.
Calories by Banana Size
Banana sizes range more than most people realize. A small banana (about 6 inches) has around 90 calories, while a large one (8 to 9 inches) climbs to roughly 121 calories. Here’s how the sizes break down:
- Extra small (under 6 inches, ~81g): 72 calories
- Small (6–7 inches, ~101g): 90 calories
- Medium (7–8 inches, ~118g): 105 calories
- Large (8–9 inches, ~136g): 121 calories
- Extra large (9+ inches, ~152g): 135 calories
If you’re measuring bananas for baking, one cup of sliced banana (150 grams) has about 134 calories. One cup of mashed banana (225 grams) has about 200 calories.
What’s Inside Those Calories
Nearly all the calories in a banana come from carbohydrates. A medium banana has about 27 grams of total carbs, including roughly 14 grams of sugar and 3 grams of fiber. There’s about 1 gram of protein and almost no fat.
Beyond the macros, bananas pack a surprising amount of micronutrients. A single medium banana delivers 422 milligrams of potassium (about 10% of your daily value), more than 30% of your daily vitamin B6, and about 10% of your daily magnesium. The potassium content is what bananas are best known for nutritionally, and it’s genuinely high compared to most fruits.
How Bananas Compare to Other Fruits
Bananas are more calorie-dense than many popular fruits, mostly because they contain less water. A medium apple (125 grams) has about 65 calories, and a medium orange (180 grams) has about 85 calories. Bananas carry more sugar per serving too: roughly 27.5 grams in a large banana compared to 13 grams in an apple and 16.8 grams in an orange. On the upside, bananas also deliver more fiber per serving, at about 5.9 grams for a large banana versus 3 grams for an apple and 4.3 grams for an orange.
Ripeness Changes the Sugar, Not the Calories
A green banana and a spotted brown banana have essentially the same number of calories. What changes dramatically is the type of carbohydrate inside. When a banana is unripe, much of its carbohydrate exists as starch, including resistant starch, which your body digests slowly or not at all. As the banana ripens, enzymes convert that starch into simple sugars like fructose and glucose. This is why a ripe banana tastes so much sweeter and feels softer.
The numbers are striking. Slightly ripe bananas contain about 4.5 grams of starch per 100 grams of fruit. By the time they’re overripe and heavily spotted, that drops to under 0.5 grams. Meanwhile, total sugar content sits around 15 to 17 grams per 100 grams regardless of ripeness stage, because the sugars are simply replacing the starch that breaks down. Fiber content also drops with ripening: from about 5 grams per 100 grams in slightly ripe fruit down to about 2 grams in overripe bananas.
Blood Sugar and Satiety
A ripe banana has a glycemic index of about 51, which puts it in the low-GI category. Green bananas score even lower, in the 30 to 40 range, because their resistant starch is absorbed more slowly. The glycemic load of a typical serving is around 13, which is moderate. So while bananas do contain natural sugar, they don’t spike blood glucose as sharply as their sweet taste might suggest.
The resistant starch in greener bananas also has a notable effect on appetite. During digestion, resistant starch gets fermented in the gut and triggers the release of hormones that signal fullness, which can reduce how much you eat at your next meal. One study found that regular consumption of green banana flour significantly increased feelings of satiety, while another found that green banana starch supplementation led to modest weight loss without any changes in diet or exercise. Resistant starch also provides fewer usable calories than regular starch, roughly half as much energy per gram.
Potassium and Kidney Health
The high potassium in bananas is a benefit for most people, but it’s worth noting for anyone with reduced kidney function. A single small banana contains about 362 milligrams of potassium, which is classified as a high-potassium food. People with kidney disease typically need to keep their daily potassium intake between 2,000 and 2,500 milligrams, so even one banana takes up a meaningful portion of that budget. If you have kidney concerns, your doctor will monitor your potassium levels and let you know when dietary limits become necessary.