Article — Flight Radiation Calculator
A typical eight-hour transatlantic flight at 35,000 ft delivers roughly 50–80 microsieverts of cosmic radiation — about one to two weeks of average natural background, or one-fortieth of a routine brain CT scan. The dose comes from galactic cosmic rays that the atmosphere normally absorbs but which thin out fast at cruise altitude. The variables that move the number are altitude, latitude, solar activity, and time spent in cruise. For occasional travellers it is a non-issue; for long-haul aircrew it can reach 2–5 millisieverts a year, which puts them in the occupational-radiation category in the EU.
This article explains what the dose is, how altitude and latitude shift it, what the numbers look like for aircrew, and which widely repeated worries about flight radiation are not supported by the data.
What flight radiation actually is
The radiation you absorb at cruise altitude is not from the aircraft. It is galactic cosmic radiation — mostly high-energy protons (about 85%), with helium nuclei (about 12%), and a small percentage of heavier ions. These particles stream in from outside the solar system, smash into atoms in the upper atmosphere, and produce showers of secondary particles (muons, neutrons, electrons, photons) that rain downward.
At sea level the atmosphere shields you from about 99% of this flux. At 35,000 ft you have lost most of that shield, and the dose rate climbs by a factor of roughly 200–300 compared with ground level. The NCRP and EPA both put the U.S. average annual cosmic-ray dose at the ground at about 330 μSv. At cruise altitude the rate jumps to around 2–3 μSv per hour — small in absolute terms, but enough to add up across a long career of flying.
Cosmic rays were discovered in 1912 by Austrian physicist Victor Hess. He flew a balloon to 5,300 m carrying electroscopes and found that ionising radiation increased with altitude, the opposite of what would happen if the source were the Earth. The work won him the 1936 Nobel Prize in Physics.
Why altitude dominates the dose
Dose rate scales roughly as altitude to the power of 1.8. Doubling altitude does not double the dose; it more than triples it. A flight at 30,000 ft picks up about 1.6 μSv per hour; at 40,000 ft the same hour gives about 2.7 μSv. That is why business jets cruising in the high 40,000s — closer to the stratosphere — produce noticeably more cosmic dose per hour than airliners in the mid-30,000s.
Concorde, which cruised at 60,000 ft (18,300 m), routinely measured 12–15 μSv/h. Its on-board radiation meter would trigger an alarm during solar particle events, prompting the pilot to descend — one of the few civil aircraft that ever did this. The current generation of high-altitude business jets (e.g. the Gulfstream G700 at 51,000 ft) sits above most weather and most other traffic, with cosmic dose roughly 50% higher per hour than mainline aircraft.
- 10,000 ft (~3,000 m) — ~0.05 μSv/h, about 15× sea level
- 20,000 ft (~6,100 m) — ~0.5 μSv/h
- 30,000 ft (~9,100 m) — ~1.6 μSv/h
- 35,000 ft (~10,700 m) — ~2.1 μSv/h (typical airliner cruise)
- 40,000 ft (~12,200 m) — ~2.7 μSv/h
- 60,000 ft (~18,300 m) — ~12 μSv/h (Concorde regime)
Latitude, polar routes, and dose variation
The Earth’s magnetic field acts as a second shield. It deflects most low- and medium-energy cosmic particles, but the deflection is strongest near the equator (where field lines run roughly horizontal) and weakest near the poles (where they dive into the ground). The effect is large: a polar flight at 11,000 m can deliver almost twice the dose rate of an equatorial flight at the same altitude.
This is why polar routes between northern Europe and East Asia (London to Tokyo, Frankfurt to Hong Kong) show up at the top of crew-dose tables — not because the planes fly higher, but because the magnetic latitude is high. Carriers running these routes monitor space weather actively and re-route south during major solar particle events.
During a strong solar particle event (e.g. the January 2005 GLE69 event), dose rate at 11,000 m and high latitude can briefly reach 100× the quiet-Sun value. Major airlines re-route polar flights southward and lower flight levels when SPE warnings are issued by NOAA SWPC and the FAA. For passengers this is operational, not a hazard you action personally.
Flight radiation exposure for aircrew
For commercial airline passengers, dose from flying is essentially a curiosity. For the people doing 80–100 hours a month at cruise, it is a real occupational issue. Long-haul aircrew typically accumulate 2–5 mSv per year of cosmic dose — in the same range as nuclear power plant workers and well above the 1 mSv/year limit the ICRP sets for members of the public.
The EU Euratom directive 2013/59 (replacing the older 96/29) requires operators to assess crew dose, inform crew above 1 mSv/year, and classify them as radiation workers if they reach 6 mSv/year. The FAA in the U.S. does not yet mandate dose limits for crew but does publish guidance (Advisory Circular 120-61B) and provides the CARI-7A dose calculator. ICRP’s general occupational limit of 20 mSv/year averaged over five years (with no single year above 50 mSv) is the benchmark long-haul crew sit well below.
Large cohort studies of European and U.S. aircrew show slightly elevated rates of melanoma, breast cancer, and some leukaemias compared with the general population. The link with cosmic radiation specifically is hard to isolate because crew also have disrupted circadian rhythms, irregular UV exposure on layovers, and different smoking and screening patterns. Most epidemiologists treat cosmic dose as a contributor, not the sole driver.
Flight radiation and pregnancy
Occasional flying during pregnancy is not a measurable radiation risk. ICRP Publication 84 and the U.S. NCRP both put the dose limit for the embryo or fetus at 1 mSv over the remainder of the pregnancy once it is declared. A single transatlantic flight delivers about 0.06–0.10 mSv to the mother and roughly the same to the fetus — well inside the limit.
Pregnant aircrew, however, are routinely re-rostered to shorter or lower-altitude routes after declaration of pregnancy, precisely because the cumulative dose across a full long-haul roster could approach the fetal limit. The same regulation that protects the fetus also pushes crew to declare early.
The radiation dose from a single transatlantic flight is roughly the same as living in a modest-radon brick or stone house for one to two months. Radon in many U.S. and European homes is a much larger annual dose source than even very frequent flying.
Common flight radiation myths
Even at 100 flights per year, an average passenger accumulates 5–10 mSv on top of 2.5 mSv natural background — well inside the dose range with no measurable acute or chronic health effect for the general population. Air travel risk is dominated by accident statistics, not radiation.
Aluminium fuselages and windows offer essentially identical shielding from high-energy cosmic radiation — the particles pass through both with negligible attenuation. Seat choice does not change dose.
The dominant particles at cruise altitude are high-energy protons and neutrons. Lead is poor shielding against fast neutrons — it can actually generate more secondary radiation through nuclear interactions. The atmosphere itself, and the airframe structure, are doing most of the (modest) shielding that exists.