Banana Dose Calculator

What is the banana equivalent dose?

Bananas contain potassium, and a tiny share of all potassium is radioactive potassium-40, or K-40. The EPA says consuming one banana would deliver a total dose of 0.01 millirem (mrem), which is 0.1 microsieverts (µSv).[EPA] The University of Groningen's radiation protection glossary calls this a "mock unit": a calculated figure for the K-40 in one average banana.[Groningen] It is a yardstick built from arithmetic, not a detector reading taken after someone eats a snack.

For the longer story, read Are Bananas Radioactive?

The formula

Going from bananas to a dose, multiply:

dose in µSv = bananas × 0.1
dose in mrem = bananas × 0.01

Going from a dose to bananas, divide:

bananas = dose in µSv ÷ 0.1
bananas = dose in mrem ÷ 0.01

The EPA's pairing also gives the conversion between the two units: 1 mrem = 10 µSv. If you enter millisieverts, the tool first converts them, because 1 mSv = 1,000 µSv. The CDC's flight figure, 0.035 mSv or 3.5 mrem, lines up with both conversions.[CDC]

Everyday exposures in bananas, on paper

The millirem column holds the published figures. The microsievert and banana columns are calculated from them with the formulas above.

Why it is an imperfect yardstick

The banana dose quietly assumes that a banana adds K-40 to your body and leaves it there. Your body does not work that way. Oak Ridge Associated Universities (ORAU) says the body "maintains relatively tight homeostatic control over potassium levels," and concludes that eating foods like bananas "does not increase your annual radiation dose."[ORAU] The Groningen glossary makes a similar point: eating bananas hardly changes the committed dose in practice, because metabolism removes excess potassium through urine.[Groningen]

That is why every result here says "on paper." An x-ray or a flight is an added exposure. A banana count is only another way of writing a number. A chest x-ray equals 1,000 bananas on paper, but eating 1,000 bananas would not work like a chest x-ray. The unit is handy for getting a feel for how small a number is. It cannot show that any particular exposure is harmless.

Limits of this tool

• The annual figures are US averages and the chest x-ray figure is a typical value, so a real exam or a real year can differ.[NRC]
• The flight figure covers one trip across the United States, not every route or altitude.[CDC]
• The 0.1 µSv figure is a rounded yardstick. Our sources give no banana size or method for it, and real bananas vary.
• The tool does simple unit arithmetic. It does not account for your body, your health, the type of radiation or how a dose was delivered.
• It accepts 0.001 to 1 trillion bananas, or the same range as a dose. Those limits are only for readable numbers and say nothing about what is safe.
• Large counts are drawn with a labeled scale, so the picture is not to scale. Trust the numbers in the results, not the size of the fruit.

What this tool is not

This tool is not a medical, radiation safety or professional determination, and its results should not be used as one. It cannot tell you what dose you received or whether an exposure is safe, and it is not advice about what to eat or avoid. If you have a question about your own exposure, ask your health care provider or a qualified radiation professional.

Want to try something else? Head back to the Science Lab.