Medium banana Size & Weight

A medium banana is about 18 cm (7 in) long along the curve, 30 – 40 mm across, and weighs roughly 118 grams with the peel (about 100 g peeled). Supermarket bananas are graded by length, and a “medium” sits between 7 and 8 inches.

This guide covers the average banana dimensions, how the grading works, why a banana is a rough but handy unit of scale, and how it compares to a pencil, a phone, and a hand.

Quick Answer: How Big Is a Medium Banana?

A medium (7 – 8 inch) banana is about 178 – 200 mm long measured along the outer curve, 30 – 40 mm in diameter, and weighs 118 – 140 g unpeeled. The edible flesh is about 100 – 118 g.

Banana Dimensions at a Glance

• Length: measured along the curve; a “medium” is 7 – 8 in (178 – 203 mm)
• Diameter: 30 – 40 mm at the thickest point, tapering toward both ends
• Curve: the fruit bends 20 – 40 degrees as it grows upward toward light
• Peel: about 12% of the total weight
• Grades (US retail): extra small under 6 in, small 6 – 7 in, medium 7 – 8 in, large 8 – 9 in, extra large over 9 in

What Does a Banana Look Like in Size?

A medium banana is a little longer than a standard pencil and about the length of an adult hand from wrist to fingertip. Laid next to a smartphone it is 30 – 50 mm longer. Its diameter is close to that of a golf ball.

6 Everyday Comparisons for a Banana

1. A #2 pencil (190 mm unsharpened) is about 10 mm longer than a medium banana.
2. An adult male hand (189 mm, wrist to fingertip) is almost the same length.
3. An iPhone 15 (147.6 mm) is about 30 – 50 mm shorter than the banana.
4. A 30 cm ruler is roughly 1.7 medium bananas laid end to end.
5. A golf ball (42.7 mm) is a bit wider than a banana’s thickest point.
6. A US dollar bill (156 mm) is close to a banana’s straight-line length.

Banana Size in Different Units

The “Banana for Scale” Convention

Online, a banana is often placed next to an object to show its size, because bananas are familiar and roughly consistent. It is a loose unit: a medium banana is about 18 cm long, so “two bananas” is roughly 36 cm and “half a banana” about 9 cm. It is good for a quick sense of scale, not for precise measurement, since a real banana can be anywhere from 6 to 10+ inches.

Common Mistakes When Comparing Banana Dimensions

1. Measuring straight across instead of along the curve. The curve adds 15 – 25 mm over the straight-line length.
2. Quoting one weight. With peel it is 118 – 140 g; peeled it is 100 – 118 g, and the USDA “medium” reference is 118 g.
3. Assuming grocery bananas are one size. They are graded by length from extra small to extra large.
4. Confusing dessert bananas with plantains. Plantains are longer (often 25 – 30 cm) and thicker.
5. Using “a banana” as an exact unit. It varies enough that it is a rough guide only.

Frequently Asked Questions

How long is a banana?

A medium banana is about 18 cm (7 in) along the curve; grades run from under 6 in to over 9 in.

How much does a banana weigh?

About 118 g with the peel, roughly 100 g peeled.

How wide is a banana?

About 30 – 40 mm at the thickest point.

How much of a banana is peel?

Roughly 12% of the total weight.

Is a banana a good unit of measurement?

As a rough visual scale, yes; for anything precise, no, because sizes vary widely.

How long is a plantain compared to a banana?

Plantains are usually longer, often 25 – 30 cm, and thicker.

Final Takeaway

A medium banana is about 18 cm (7 in) long along the curve, 30 – 40 mm across, and 118 grams with the peel. Supermarket bananas are graded by length from extra small to extra large, so “a banana for scale” is a handy but loose reference of roughly 18 cm.