How many miles of undersea internet cable are there?

How to get close to this number

Count the routes. Every pair of continents needs several independent cables for capacity and redundancy, each running thousands of miles, and there are hundreds of such cables in service. A few hundred routes averaging a few thousand miles each gives a total in the hundreds of thousands — and the explanation checks it as thirty-five times round the Earth.

The fact that upends most people's mental model is that satellites carry almost nothing. Over ninety-five percent of intercontinental traffic runs through cables on the sea floor, because fibre beats radio on both capacity and latency by enormous margins. The internet is a physical network of glass on the seabed, not a cloud.

The fragility figure is the one worth keeping: these cables are cut around two hundred times a year, mostly by ships' anchors and fishing gear in shallow water. The system survives because of redundancy rather than robustness — traffic reroutes around a break within seconds, which is why a global infrastructure that is regularly severed almost never visibly fails.