A medium banana has about 420–450 mg of potassium, which is roughly 10–12% of most adults’ daily needs.

Here’s a quick breakdown:

  • Small banana (around 6 inches): about 350–360 mg potassium.
  • Medium banana (7–8 inches, the usual “reference” size): about 420–450 mg potassium.
  • Large banana (8–9 inches): can approach or slightly exceed 480–500 mg potassium.

In everyday terms, if someone says “a banana has 400-ish milligrams of potassium,” they’re talking about a typical medium fruit and are basically right.