Answer & explanation
The official answer, with Fermi’s reasoning step by step.
Answer & explanation
Official answer
5
hours
How to estimate it
Fermi’s official “Napkin math”
The Channel is about 34 kilometers at its narrowest. How fast does a world record swimmer move? A quick 100 meters takes about 50 seconds, which works out to 7 kilometers an hour.
- Channel crossing
- ~34 km
- Phelps' pace
- ~7 km/h
- 34 ÷ 7
- ≈ 4.9 hours
The Channel is about 21 miles at its narrowest. How fast does a world record swimmer move? Way slower than running, even for him. Call it 4 miles an hour.
- Channel crossing
- ~21 miles
- Phelps' pace
- ~4 mph
- 21 ÷ 4
- ≈ 5.3 hours
Rounded assumptions may give a slightly different estimate. The official answer above is the game’s reference value.
Source calculation & reference
- Straight-line crossing, Shakespeare Beach to Cap Gris-Nez
- 21 miles (33.8 km)
- Phelps' 200 m freestyle world record, Beijing 2008
- 1:42.96, or 1.94 m/s
- 33,800 m ÷ 1.94 m/s
- ≈ 17,400 seconds
- ≈
- 4.8 hours, rounded to 5
Reference cited by Fermi: Channel Swimming Association crossing distance · World Aquatics world record progression for the men's 200 m freestyle
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