How this calculator works
At cruise altitude the atmosphere shields less of the cosmic radiation that arrives from space, so the dose rate is higher than at sea level. The total dose on a flight is approximately the average dose rate multiplied by the time in the air. Dose rate depends strongly on altitude, latitude and the solar cycle: a long polar route at 39,000 feet can receive several times the dose of a short equatorial flight. This page uses the average rate you enter, so it cannot capture a route that climbs, changes latitude or sees a solar event. It estimates the flight dose only; it does not include radon, medical exposure or ground-level background.
Formula
dose = dose rate x time. Dose in mrem = dose in microSv / 10, because 1 mSv = 100 mrem and 1 mSv = 1,000 microSv. To reverse it, dose rate = dose / time and time = dose / dose rate.
Worked example
A six-hour flight at an average of 4 microSv/h gives 24 microSv, which is 2.4 mrem. Twelve hours at 5 microSv/h gives 60 microSv, or 6 mrem.
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Frequently asked questions
Is this a safety limit?
No. It is an arithmetic estimate of the dose from one flight. Occupational limits for aircrew are set by regulators, and the FAA advises a five-year average of 20 mSv per year with no single year above 50 mSv. Compare any concern with the applicable guidance, not with this page.
What dose rate should I use for a short flight?
Short flights spend less time at cruise altitude, so their average rate is lower. A rough long-haul cruise figure is 4 to 5 microSv/h at mid-latitudes, lower near the equator and higher on polar routes. Use a route-specific value if you have one.
Does the calculator include the return flight?
No. It reports one flight. Double the time or add the two flight times separately to estimate a round trip.
Why are doses quoted in both microSv and mrem?
Sieverts are the SI unit and rem is the older unit still common in the United States. The conversion is exact: 1 Sv = 100 rem, so 1 microSv = 0.1 mrem.