Answer & explanation
The official answer, with Fermi’s reasoning step by step.
Answer & explanation
Official answer
171
watches
How to estimate it
Fermi’s official “Napkin math”
We have to guess the size of a Submariner and one of Big Ben's faces. The Submariner is easy since it's a watch and you can use your wrist as reference: it's around a couple inches. The face of Big Ben is harder, and probably bigger than it looks. Maybe 20 feet?
- Big Ben's face
- ~20 ft = 240 in
- Submariner, across
- ~2 in
- 240 ÷ 2
- ≈ 120
We have to guess the size of a Submariner and one of Big Ben's faces. The Submariner is easy since it's a watch and you can use your wrist as reference: it's around 5 centimeters. The face of Big Ben is harder, and probably bigger than it looks. Maybe 6 meters?
- Big Ben's face
- ~6 m = 600 cm
- Submariner, across
- ~5 cm
- 600 ÷ 5
- ≈ 120
Rounded assumptions may give a slightly different estimate. The official answer above is the game’s reference value.
Source calculation & reference
- Clock dial diameter (UK Parliament)
- 7 m
- Submariner Date case (Rolex)
- ÷ 41 mm
- 7,000 ÷ 41
- ≈ 170.7
- 170 falls short, so it takes
- 171 watches
Reference cited by Fermi: UK Parliament and Rolex
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