How Much Radiation Have I Been Exposed To?

Every second, cosmic rays, the ground beneath you, and even the food on your plate are quietly depositing tiny amounts of radiation into your body. It's been happening since before you were born and keeps happening no matter where you live. The calculator above turns your birth date into a running total: the average person in the US picks up about 3.1 millisieverts (mSv) a year from natural background sources alone.

That number sounds abstract until you translate it into something familiar: bananas. Every banana contains a trace of radioactive potassium-40, so scientists use the banana equivalent dose as a tongue-in-cheek teaching unit — one banana is about 0.1 microsieverts. Stack up a lifetime of ordinary background exposure and you're talking about well over a million bananas by middle age.

None of this is cause for worry. These are the same doses that airline crews, Denver residents, and everyone who has ever eaten a banana absorb as a matter of course. What follows explains where the number comes from, what it leaves out (medical imaging roughly doubles it), and how the pieces add up.

Measured in bananas

Radon gas is the single biggest contributor to natural background radiation, accounting for roughly two-thirds of the average American's dose. It seeps out of soil and rock and collects indoors, especially in basements and lower floors, which is why radon is the background source most tied to a given home rather than to geography. The rest comes from cosmic rays raining down from space (stronger at altitude, which is why Denver runs higher than a coastal city), terrestrial radiation from rock and soil, and internal sources — potassium-40 and trace radioactive elements already built into your own tissue.

Add it up and the US average lands near 3.1 mSv a year. Medical imaging is a separate bucket: X-rays, CT scans, and other diagnostic tests contribute roughly another 3 mSv a year on average nationally, nearly doubling total exposure — but that dose is optional, occasional, and not part of the background number this calculator tracks.

How the calculator works

The calculator takes your age in years and multiplies it by 3.1 mSv, the US average annual dose from natural background radiation. That figure bundles radon, cosmic rays, terrestrial sources, and the radioactive potassium and carbon already inside your body.

To make the total tangible, the same number is converted into two familiar comparisons: banana equivalent doses (dividing by 0.1 microsieverts per banana) and chest X-rays (dividing by roughly 0.1 mSv per scan).

This is a population average, not a personal dosimeter reading. It leaves out medical imaging entirely, and it can't account for where you actually live: someone in Denver's thin air or a radon-heavy basement absorbs meaningfully more than someone at sea level in a well-ventilated home. Treat the result as a reasonable ballpark, not a lab measurement.