The average person receives about 6 millisieverts (mSv) of radiation per year, which works out to roughly 0.016 mSv per day. About half of that comes from natural background sources you can’t avoid, and the other half comes from medical procedures like X-rays and CT scans. That daily number shifts depending on where you live, how often you fly, and whether you’ve had any imaging done recently.
What 0.016 mSv Per Day Actually Means
A millisievert is the standard unit for measuring how much radiation energy your body absorbs. At 0.016 mSv per day, you’re absorbing a tiny amount of energy from multiple directions at once: the ground beneath you, the sky above you, the food you eat, and even radioactive elements inside your own body. This baseline exposure has existed for as long as humans have, and your cells have repair mechanisms that handle damage at these levels without trouble.
To put that daily dose in perspective, a single chest X-ray delivers about 0.02 mSv, roughly equivalent to one day of background radiation. A chest CT scan, on the other hand, delivers about 7 mSv, which is more than a full year of natural background exposure compressed into a few seconds. The international standard for public safety, set by the International Commission on Radiological Protection, caps additional exposure from artificial sources (not counting medical care) at 1 mSv per year.
The Four Natural Sources
Natural background radiation accounts for about 3 mSv per year, and it breaks down into four categories. Radon gas is the largest single contributor, responsible for roughly half of all natural exposure. Cosmic rays from space add about 0.27 mSv per year at sea level. Radioactive elements in soil, rock, and building materials contribute around 0.28 mSv per year. And naturally radioactive atoms inside your own body, primarily a form of potassium, add another 0.14 mSv per year.
Of these, radon deserves the most attention because it’s the one you can actually do something about. Radon is an odorless gas that seeps up from the ground into homes through cracks in foundations. The average American home has a radon concentration of about 1.3 picocuries per liter (pCi/L). The EPA recommends fixing your home if levels reach 4 pCi/L or higher, and suggests considering action even between 2 and 4 pCi/L, because there’s no known safe threshold for radon exposure. Inexpensive test kits are available at most hardware stores.
How Altitude Changes Your Dose
Cosmic radiation increases significantly with altitude because there’s less atmosphere above you to absorb it. At sea level, the exposure rate from cosmic rays is about 0.06 microsieverts per hour. At 35,000 feet, the cruising altitude of most commercial flights, that rate jumps to roughly 6 microsieverts per hour, about 100 times the sea-level rate.
A transatlantic flight between Europe and North America typically delivers between 4 and 8 microsieverts per hour, meaning a seven-hour flight adds somewhere around 0.03 to 0.06 mSv to your total. That’s two to four days’ worth of ground-level background radiation absorbed over the course of one flight. Frequent flyers and airline crew accumulate noticeably more cosmic radiation over the course of a year than people who rarely fly, though the total still falls well within safe limits for most.
Living at high altitude also increases your daily dose, though less dramatically than flying. Cities like Denver sit about a mile above sea level, and residents there receive measurably more cosmic radiation year-round than someone living in a coastal city like Miami. The difference isn’t large enough to pose a health concern, but it’s one reason your personal daily dose may differ from the national average.
Medical Imaging Is the Biggest Variable
The other 3 mSv of the average person’s annual exposure comes from medical procedures, but that number is just an average. If you didn’t have any imaging done this year, your medical contribution is zero. If you had a CT scan, you may have received more than the entire “average” annual total in a single visit.
Here’s how common procedures compare:
- Chest X-ray: 0.02 mSv (about one day of background radiation)
- Dental X-ray: 0.005 to 0.01 mSv (a few hours of background)
- Chest CT scan: 7 mSv (more than a year of natural background)
These doses are considered medically justified when the diagnostic information they provide outweighs the small additional risk. But they’re worth being aware of, especially if you’re getting multiple scans over a short period. The radiation from an X-ray or CT doesn’t linger in your body. It passes through in the moment the image is taken.
Household Items and Building Materials
You may have heard concerns about radiation from granite countertops, concrete, or brick. These materials do contain trace amounts of naturally radioactive elements, but the CDC notes that radiation levels from building materials are very low and highly unlikely to increase your dose above normal background levels. The more relevant concern with certain building materials is that they can contribute to indoor radon accumulation, which circles back to radon testing as the practical step worth taking.
Smoke detectors contain a tiny amount of radioactive material, but the dose they deliver to anyone in the room is negligible. In practical terms, no common household product meaningfully changes your daily radiation exposure.
Putting Your Personal Exposure in Context
Your actual daily dose depends on a handful of factors: your home’s radon level, your altitude, how much you fly, and whether you’ve had recent medical imaging. Someone living in a low-radon home at sea level who skipped the doctor this year might absorb closer to 2 mSv total for the year, or about 0.005 mSv per day. Someone living at altitude in a home with elevated radon who also had a CT scan could easily exceed 10 mSv for the year.
The one factor most worth checking is radon, since it’s the largest natural contributor and the only one you can reduce at home. Everything else, cosmic rays, trace radiation in soil, the potassium in your own bones, is a fixed part of living on a mildly radioactive planet.