The 2011 Japan (Tōhoku) tsunami reached about 40 meters (around 130 feet) high at its largest, and commonly 10–20 meters (30–65 feet) along much of the hardest‑hit coast.

How big was the tsunami?

  • Peak height: Up to about 40–40.5 meters (around 130–133 feet) in parts of Iwate Prefecture (for example near Miyako).
  • Typical large run‑up: Many coastal areas saw waves roughly 10–20 meters high (30–65 feet), easily overtopping seawalls.
  • Distance inland: In the Sendai plain, the water traveled up to about 10 km (around 6 miles) inland.
  • Flooded area: More than about 500 square kilometers (roughly 200 square miles) of coastline were flooded in northeastern Honshu.

Put simply, this was an extremely large tsunami by modern standards, strong enough to erase entire towns.

Quick event snapshot

  • Date: March 11, 2011, off northeast Honshu, Japan.
  • Trigger: A magnitude 9.0–9.1 megathrust earthquake on the Japan Trench (the strongest ever recorded in Japan).
  • Speed: In deep water near Sendai, the tsunami waves traveled at roughly 700 km/h (about 435 mph) before slowing and growing taller near shore.

These numbers are why it is often described as one of the most powerful tsunamis ever recorded.

Human and wider impact (brief)

  • Deaths and missing: More than about 18,000 people were killed or went missing.
  • Towns: Entire coastal communities were destroyed as the water overtopped defenses and swept far inland.
  • Nuclear disaster: Flooding knocked out power and cooling at the Fukushima Daiichi nuclear plant, causing a major nuclear accident.

One way people on the ground described it: they’d been told to expect a 3‑meter wave; what arrived in some places was over ten times that height.

Mini table: key “size” facts (HTML)

[1][5][3] [10][5][7][3] [5][3] [5] [10][7][9][3][5]
Measure Approximate value
Maximum tsunami height ~40–40.5 m (130–133 ft) in parts of Iwate Prefecture
Typical large coastal heights ~10–20 m (30–65 ft) along many sections of the Tōhoku coast
Inland penetration Up to ~10 km (6 mi) inland on the Sendai plain
Flooded coastal area >500 km² (~200 mi²) inundated
Earthquake magnitude 9.0–9.1 (megathrust), strongest ever recorded in Japan
**TL;DR:** The 2011 Japan tsunami was colossal, with peak heights around 40 meters, widespread 10–20 meter waves, and water reaching up to 10 km inland.

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