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

Reverse: Johannesburg → London

A flight from London Heathrow Airport to O.R. Tambo International Airport at 35,000 ft, about 10 h 36 min in the air, receives about 0.0216 mSv (21.6 µSv) of cosmic radiation: about a fifth 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
21.6 µSv0.0216 mSv
Time in the air
10 h 36 minestimated
Dose rate
2.0 µSv/haverage, 35,000 ft
Chest X‑rays
0.22at 0.1 mSv each

Key facts: LHR → JNB

Dose, standard flight0.0216 mSv (21.6 µSv)
Time in the air10 h 36 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 36 min in the air (climb 25 min, cruise 594 min, descent 17 min), effective dose per ICRP Publication 103. How it's calculated.

LHRJNB
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 LHR → JNB

The sun's 11-year cycle moves this number. With the same 10 h 36 min at 35,000 ft, the flight would have received 0.0234 mSv in April 2020, when the sun was quiet and more galactic cosmic rays reached the atmosphere, and 0.0196 mSv in January 2026, near solar maximum: 19% more at the quiet end. In August 2026 it is 0.0216 mSv.

Dose for this flight at 35,000 ft, quarterly
0 µSv10 µSv20 µSv30 µSv20162018202020222024202623.4 µSv19.6 µSv21.6 µSv
0 µSv10 µSv20 µSv30 µSv20162020202423.4 µSv19.6 µSv21.6 µSv
The numbers behind the chart
MonthDoseDose
January 201622.4 µSv0.0224 mSv
April 201622.6 µSv0.0226 mSv
July 201622.6 µSv0.0226 mSv
October 201622.8 µSv0.0228 mSv
January 201722.9 µSv0.0229 mSv
April 201723.1 µSv0.0231 mSv
July 201723 µSv0.023 mSv
October 201722.9 µSv0.0229 mSv
January 201823 µSv0.023 mSv
April 201823.2 µSv0.0232 mSv
July 201823.2 µSv0.0232 mSv
October 201823.3 µSv0.0233 mSv
January 201923 µSv0.023 mSv
April 201923.3 µSv0.0233 mSv
July 201923.2 µSv0.0232 mSv
October 201923.3 µSv0.0233 mSv
January 202023.3 µSv0.0233 mSv
April 202023.4 µSv0.0234 mSv
July 202023.3 µSv0.0233 mSv
October 202023.3 µSv0.0233 mSv
January 202123 µSv0.023 mSv
April 202123.3 µSv0.0233 mSv
July 202123.2 µSv0.0232 mSv
October 202123.2 µSv0.0232 mSv
January 202223 µSv0.023 mSv
April 202222.9 µSv0.0229 mSv
July 202222.2 µSv0.0222 mSv
October 202222.5 µSv0.0225 mSv
January 202321.8 µSv0.0217 mSv
April 202321.9 µSv0.0219 mSv
July 202321.4 µSv0.0214 mSv
October 202321.4 µSv0.0214 mSv
January 202420.9 µSv0.0209 mSv
April 202421.1 µSv0.0211 mSv
July 202421.2 µSv0.0212 mSv
October 202420 µSv0.02 mSv
January 202520.4 µSv0.0204 mSv
April 202520.4 µSv0.0204 mSv
July 202520.3 µSv0.0203 mSv
October 202520.5 µSv0.0205 mSv
January 202619.6 µSv0.0196 mSv
April 202620.6 µSv0.0206 mSv
July 202621.2 µSv0.0212 mSv
August 202621.6 µSv0.0216 mSv

How cruise altitude changes the dose

Flown at 31,000 ft instead, the same flight would receive 0.0162 mSv, 25% less than at 35,000 ft; at 41,000 ft it would receive 0.0294 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 ft16.2 µSv
  • 33,000 ft18.8 µSv
  • 35,000 ft21.6 µSv
  • 37,000 ft24.3 µSv
  • 39,000 ft27 µSv
  • 41,000 ft29.4 µSv

Try it: change the altitude and the month

Every combination is its own CARI-7 run for LHR → JNB, with the same 10 h 36 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 ft16.817.217.317.217.417.317.316.315.715.314.716.2
33,000 ft19.52020.12020.320.120.11918.317.817.118.8
35,000 ft22.422.9232323.3232321.820.920.419.621.6
37,000 ft25.225.92625.926.3262624.523.622.92224.3
39,000 ft2828.728.928.829.228.928.827.226.125.424.427
41,000 ft30.631.331.531.431.931.531.529.728.527.726.629.4

The return flight: JNB → LHR

JNB → LHR receives 0.0223 mSv at 35,000 ft, 3% more than LHR → JNB, over about 10 h 53 min in the air against 10 h 36 min. The return takes 17 min longer: its track runs against 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
  • LHR → JNB21.6 µSv
  • JNB → LHR22.3 µSv

Cosmic radiation on Johannesburg → London flights

What 21.6 µSv compares with

Compared withIts doseThis flight is
Chest X-Ray0.1 mSvabout a fifth of a chest X-ray
Dental X-Ray0.005 mSvabout 4.3 dental X-rays
Background Radiation (Daily)0.008 mSvabout 2.7 days of natural background radiation
Mammogram0.4 mSvabout 5% of a mammogram
Head CT Scan2 mSvabout 1% of a head CT scan
Eating a Banana0.0001 mSvabout 216 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 0.0162 mSv, 25% less than at 35,000 ft; at 41,000 ft it would receive 0.0294 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 19% 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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