The Channel Tunnel (often called the Chunnel) reaches a maximum depth of about 75 meters (around 246 feet) below sea level at its deepest point. Relative to the seabed itself, it sits roughly 45 meters (about 148 feet) beneath the sea floor on average.

Key depth facts

  • Maximum depth: about 75 m (246 ft) below sea level.
  • Depth below seabed: on average around 45 m (148 ft) under the sea bed.
  • The tunnel’s undersea section is about 37.9–38 km long, making it the longest undersea tunnel section in the world.

Why it is that deep

Engineers placed the tunnel at this depth to keep it within stable chalk layers beneath the seabed, reducing the risk of water ingress and improving long‑term safety. Going too shallow would bring it closer to softer, more permeable strata and higher water pressures from the Channel above.

Extra context for travelers

  • You travel through this depth inside high‑speed rail tunnels linking Folkestone (UK) and Calais/Coquelles (France).
  • Despite being so deep, the ride feels similar to any other long rail tunnel; you do not feel the depth change the way you might notice altitude in a plane.

Information gathered from public forums or data available on the internet and portrayed here.