Cosmic radiation on flights from San Francisco (SFO) to Singapore (SIN)

How the sun changes the dose on SFO → SIN

The sun's 11-year cycle moves this number. With the same 16 h 42 min at 35,000 ft, the flight would have received 0.0476 mSv in April 2020, when the sun was quiet and more galactic cosmic rays reached the atmosphere, and 0.0368 mSv in January 2026, near solar maximum: 29% more at the quiet end. In August 2026 it is 0.0424 mSv.

How cruise altitude changes the dose

Flown at 31,000 ft instead, the same flight would receive 0.0315 mSv, 26% less than at 35,000 ft; at 41,000 ft it would receive 0.0589 mSv, 39% more. Same route, same time in the air, same month: only the air overhead changes.

Try it: change the altitude and the month

Every combination is its own CARI-7 run for SFO → SIN, with the same 16 h 42 min in the air. It is still a standard flight, not yours: the app calculates your exact flight.

The return flight: SIN → SFO

SIN → SFO receives 0.0391 mSv at 35,000 ft, 8% less than SFO → SIN, over about 15 h 24 min in the air against 16 h 42 min. The return is 1 h 18 min shorter: its track runs with the prevailing westerly winds at cruise altitude. Cosmic radiation builds up with every minute aloft, so the longer direction collects more of it along the same path.

Cosmic radiation on Singapore → San Francisco flights

What 42.4 µSv compares with

The comparison values are the ones the FlightDose app uses.

Questions people ask

• AircrewHow much radiation do pilots and flight attendants get?
• Flight vs X-rayIs a flight more radiation than an X-ray?
• PregnancyIs the radiation from flying safe in pregnancy?
• Solar stormsDo solar storms make flying more dangerous?

All questions