Annual Radiation Dose Calculator
This calculator estimates your annual effective radiation dose in millisieverts (mSv) from all major sources: natural background radiation, medical imaging, air travel, and everyday life. Fill in the sections that apply to you and your total updates instantly. The U.S. population average is about 6.2 mSv per year (620 mrem). Results are an educational estimate, not a clinical measurement.
What is effective radiation dose?
Effective dose, measured in millisieverts (mSv), is a single number that captures both the energy deposited in tissue by ionizing radiation and the biological sensitivity of the organs exposed. It lets scientists compare wildly different exposure scenarios on a common scale, a chest X-ray, a CT scan, and a year of cosmic-ray exposure can all be expressed in mSv. The U.S. annual average of 6.2 mSv comes roughly half from natural sources (mostly radon) and half from medical imaging, which has grown substantially since CT scanning became routine. The older U.S. unit, the millirem, is simply 1/100 of a milliSievert, so 6.2 mSv equals 620 mrem.
Where does my radiation come from?
For most Americans, radon gas seeping into buildings from uranium-bearing soils is the single largest source, contributing about 2.28 mSv per year on average, but this varies enormously by geography and home construction. Cosmic rays from space add more at higher elevations: Denver (5,280 ft) residents receive roughly twice the cosmic dose of someone at sea level. Naturally occurring radionuclides in food, water, and your own body tissues (principally potassium-40) add a fixed 0.29 mSv that cannot be avoided. Medical imaging now accounts for about 48% of the total U.S. average, driven largely by CT scanning. A single abdominal CT equals several years of background exposure.
Is my dose dangerous?
Radiation risk at everyday doses is real but small and difficult to measure directly. The linear no-threshold (LNT) model, used by most regulatory agencies, assumes that risk scales proportionally with dose even at low levels, though this remains debated in radiobiology. The ICRP sets a 1 mSv/year public limit (above natural background) as a conservative precaution; U.S. radiation workers are allowed up to 50 mSv/year. At the U.S. population average of 6.2 mSv, the estimated lifetime excess cancer risk is in the range of a few tenths of a percent, far below the background cancer risk of about 40%. Radon at high indoor concentrations is a proven lung-carcinogen and is the actionable risk for most people. Testing your home costs under $30 and mitigation systems typically reduce levels by 80 percent or more.
How to reduce your radiation dose
The most impactful steps for most people are: (1) Test your home for radon, especially if you live in the Midwest, Mountain West, or Pennsylvania, where soil uranium levels are highest. Mitigation is highly effective. (2) Question CT scans when simpler imaging (ultrasound, MRI, plain X-ray) could answer the clinical question. ALARA ("as low as reasonably achievable") is a guiding principle in medical practice. (3) If you smoke, each pack-year adds roughly 70 mSv directly to lung bronchial epithelium - the largest controllable radiation risk for most individuals. (4) Air travel exposes you to elevated cosmic radiation, but even a 200-hour-per-year frequent flier adds only about 0.8 mSv, well within safe ranges. Building your home in stone or brick rather than wood adds a small amount; no lifestyle change is needed for that factor.
Typical radiation doses by source
| Source | Dose (mSv) | Equivalent to |
|---|---|---|
| U.S. average annual dose (all sources) | 6.2 | 100% |
| Natural background (avg, no radon) | 0.83 | 13% of total avg |
| Average indoor radon | 2.28 | 37% of total avg |
| Chest X-ray | 0.1 | 10 days of background |
| Dental X-ray | 0.005 | 1 day of background |
| Mammogram | 0.4 | 7 weeks of background |
| CT scan - head | 2.0 | 8 months of background |
| CT scan - chest | 7.0 | 2.3 years of background |
| CT scan - abdomen/pelvis | 8.0 | 2.7 years of background |
| PET scan | 14.1 | 4.7 years of background |
| Transatlantic flight (8 hrs) | 0.03 | 3 days of background |
| Smoking 1 pack/day | 70 | 11 times the avg yearly dose |
| NRC occupational limit | 50/yr | Per-year cap for radiation workers |
| ICRP public limit | 1/yr (excl. natural) | Above background limit for public |
Representative effective dose values. Individual exposures vary.
Frequently asked questions
What is a millisievert (mSv)?
The millisievert is the SI unit of effective radiation dose. It accounts not just for how much radiation energy is absorbed, but also for which tissues are exposed and the type of radiation involved. One mSv equals 100 millirem (mrem), the older U.S. unit. The U.S. annual per-capita dose is about 6.2 mSv (620 mrem) from all sources combined.
Is medical radiation from CT scans dangerous?
A single CT scan is generally low-risk compared to the benefit of the diagnosis it provides. However, CT delivers substantially more dose than plain X-rays: an abdominal CT (8 mSv) equals about 2.7 years of natural background. Multiple CT scans accumulate, and the linear no-threshold model suggests even low doses carry some theoretical excess cancer risk. Always ask your doctor whether the scan is clinically necessary, and whether ultrasound or MRI could substitute, since those modalities use no ionizing radiation.
Why is radon such a large part of my dose?
Radon is a naturally occurring radioactive gas produced by the decay of uranium in soil and rock. It seeps into buildings through foundations and accumulates indoors. The U.S. average indoor level delivers about 2.28 mSv per year, more than all other natural sources combined. Crucially, radon is also a proven carcinogen: it is the second-leading cause of lung cancer in the U.S. after smoking. Testing with a $20-30 radon kit is the single most cost-effective radiation-safety action most homeowners can take.
How much radiation does a flight add?
At cruising altitude (35,000-39,000 ft) the cosmic ray dose rate is roughly 0.004 mSv per hour, about 100 times higher than at sea level, because there is less atmosphere to shield incoming particles. A transatlantic flight of 8 hours adds about 0.03 mSv. Even a very frequent flier logging 200 hours per year receives about 0.8 mSv of flight-related exposure, well within normal limits. Airline crews who fly 800 or more hours annually can approach 3-4 mSv from travel alone, which is why they are monitored as occupationally exposed workers in some countries.
What does the U.S. NRC radiation limit mean?
The Nuclear Regulatory Commission sets a limit of 50 mSv per year (5,000 mrem) for occupationally exposed radiation workers, with a cumulative lifetime limit of 10 mSv per year of age. The public limit is 1 mSv per year above natural background from any single licensed facility. These limits are set with large safety margins and are far above what most people receive. The U.S. average dose of 6.2 mSv includes natural background and medical; it is not a limit - just the observed population average.
Why does smoking increase radiation dose?
Tobacco leaves accumulate polonium-210 and lead-210 from phosphate fertilisers. When cigarettes are smoked, these alpha-emitting radionuclides are deposited in the bronchial airways. A pack-a-day smoker delivers about 70 mSv per year directly to lung tissue, which is roughly 10 times the total average annual dose from all other sources. This is one of the reasons lung cancer risk from smoking is so high: it combines chemical carcinogens with concentrated localised radiation.