Cosmic radiation on flights from Johannesburg (JNB) to London (LHR)

Reverse: London → Johannesburg

A flight from O.R. Tambo International Airport to London Heathrow Airport at 35,000 ft, about 10 h 53 min in the air, receives about 0.0223 mSv (22.3 µSv) of cosmic radiation: about a quarter of a chest X-ray. That is the FAA's CARI-7 model run for this route with the solar conditions of August 2026.

Updated · solar conditions of August 2026

Dose
22.3 µSv0.0223 mSv
Time in the air
10 h 53 minestimated
Dose rate
2.0 µSv/haverage, 35,000 ft
Chest X‑rays
0.22at 0.1 mSv each

Key facts: JNB → LHR

Dose, standard flight0.0223 mSv (22.3 µSv)
Time in the air10 h 53 min, estimated from distance and prevailing winds
Cruise altitude35,000 ft
Average dose rate2.0 µSv/h
Great-circle distance9,075 km (5,639 mi)
Furthest from the equator51.5°N
Solar conditionsAugust 2026

The standard flight is CARI-7, the FAA Civil Aerospace Medical Institute's model, run on the dev machine for this route: 35,000 ft, 10 h 53 min in the air (climb 25 min, cruise 611 min, descent 17 min), effective dose per ICRP Publication 103. How it's calculated.

JNBLHR
Great-circle route, shaded from 1.5 µSv/h to 3.8 µSv/h. Shading is modelled from the monthly dose-rate grid; totals are CARI-7.

How the sun changes the dose on JNB → LHR

The sun's 11-year cycle moves this number. With the same 10 h 53 min at 35,000 ft, the flight would have received 0.0242 mSv in April 2020, when the sun was quiet and more galactic cosmic rays reached the atmosphere, and 0.0202 mSv in January 2026, near solar maximum: 20% more at the quiet end. In August 2026 it is 0.0223 mSv.

Dose for this flight at 35,000 ft, quarterly
0 µSv10 µSv20 µSv30 µSv20162018202020222024202624.2 µSv20.2 µSv22.3 µSv
0 µSv10 µSv20 µSv30 µSv20162020202424.2 µSv20.2 µSv22.3 µSv
The numbers behind the chart
MonthDoseDose
January 201623.1 µSv0.0231 mSv
April 201623.4 µSv0.0234 mSv
July 201623.3 µSv0.0233 mSv
October 201623.6 µSv0.0236 mSv
January 201723.7 µSv0.0237 mSv
April 201723.9 µSv0.0239 mSv
July 201723.8 µSv0.0238 mSv
October 201723.7 µSv0.0237 mSv
January 201823.8 µSv0.0238 mSv
April 201824 µSv0.024 mSv
July 201824 µSv0.024 mSv
October 201824.2 µSv0.0242 mSv
January 201923.8 µSv0.0238 mSv
April 201924.1 µSv0.0241 mSv
July 201924 µSv0.024 mSv
October 201924.1 µSv0.0241 mSv
January 202024.1 µSv0.0241 mSv
April 202024.2 µSv0.0242 mSv
July 202024.1 µSv0.0241 mSv
October 202024.1 µSv0.0241 mSv
January 202123.8 µSv0.0238 mSv
April 202124.2 µSv0.0242 mSv
July 202123.9 µSv0.0239 mSv
October 202124 µSv0.024 mSv
January 202223.8 µSv0.0238 mSv
April 202223.7 µSv0.0237 mSv
July 202223 µSv0.023 mSv
October 202223.3 µSv0.0233 mSv
January 202322.5 µSv0.0225 mSv
April 202322.6 µSv0.0226 mSv
July 202322.1 µSv0.0221 mSv
October 202322.1 µSv0.0221 mSv
January 202421.6 µSv0.0216 mSv
April 202421.8 µSv0.0218 mSv
July 202421.9 µSv0.0219 mSv
October 202420.7 µSv0.0207 mSv
January 202521 µSv0.021 mSv
April 202521 µSv0.021 mSv
July 202520.9 µSv0.0209 mSv
October 202521.2 µSv0.0212 mSv
January 202620.2 µSv0.0202 mSv
April 202621.3 µSv0.0213 mSv
July 202621.9 µSv0.0219 mSv
August 202622.3 µSv0.0223 mSv

How cruise altitude changes the dose

Flown at 31,000 ft instead, the same flight would receive 0.0167 mSv, 25% less than at 35,000 ft; at 41,000 ft it would receive 0.0304 mSv, 36% more. Same route, same time in the air, same month: only the air overhead changes.

Dose for this flight by cruise altitude, August 2026
  • 31,000 ft16.7 µSv
  • 33,000 ft19.5 µSv
  • 35,000 ft22.3 µSv
  • 37,000 ft25.1 µSv
  • 39,000 ft27.9 µSv
  • 41,000 ft30.4 µSv

Try it: change the altitude and the month

Every combination is its own CARI-7 run for JNB → LHR, with the same 10 h 53 min in the air. It is still a standard flight, not yours: the app calculates your exact flight.

Every combination as a table (µSv)
AltitudeJan 2016Jan 2017Jan 2018Jan 2019Jan 2020Jan 2021Jan 2022Jan 2023Jan 2024Jan 2025Jan 2026Aug 2026
31,000 ft17.317.817.917.818.117.917.816.916.215.815.116.7
33,000 ft20.220.720.820.72120.820.819.618.818.417.619.5
35,000 ft23.123.723.823.824.123.823.822.521.62120.222.3
37,000 ft26.126.726.926.827.226.926.925.324.323.722.725.1
39,000 ft2929.729.929.830.229.929.828.12726.325.227.9
41,000 ft31.632.432.632.53332.632.630.729.428.627.430.4

The return flight: LHR → JNB

LHR → JNB receives 0.0216 mSv at 35,000 ft, 3% less than JNB → LHR, over about 10 h 36 min in the air against 10 h 53 min. The return is 17 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.

Dose for each direction, standard flight
  • JNB → LHR22.3 µSv
  • LHR → JNB21.6 µSv

Cosmic radiation on London → Johannesburg flights

What 22.3 µSv compares with

Compared withIts doseThis flight is
Chest X-Ray0.1 mSvabout a quarter of a chest X-ray
Dental X-Ray0.005 mSvabout 4.5 dental X-rays
Background Radiation (Daily)0.008 mSvabout 2.8 days of natural background radiation
Mammogram0.4 mSvabout 6% of a mammogram
Head CT Scan2 mSvabout 1% of a head CT scan
Eating a Banana0.0001 mSvabout 223 bananas

The comparison values are the ones the FlightDose app uses.

Why your flight will differ

  • Altitude. Flown at 31,000 ft instead, the same flight would receive 0.0167 mSv, 25% less than at 35,000 ft; at 41,000 ft it would receive 0.0304 mSv, 36% more. Same route, same time in the air, same month: only the air overhead changes.
  • Time in the air. Every extra 30 minutes on this route adds about 1 µSv. Headwinds, holding and routing change it by tens of minutes on a long flight.
  • The month. The sun's 11-year cycle swings this route's dose by about 20% between quiet and active years.
  • The track. Airlines fly tracks that bend with the jet stream, not the exact great circle; a track further from the equator collects more.
  • Solar storms. A rare solar radiation storm can add to the dose for hours; CARI-7's monthly figures don't include one.

FlightDose calculates your exact flight.

Your date, your altitude, your time in the air, with live space weather, and a running total against the limits that matter to you.

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