NHK reporting that after analysis of the range of destruction by the March 11 tsunami, plus the fact that most 10 meter tall sea walls failed,  the tsunami must have been more than 20 meters high.

Here in the U.S. that’s 65.5 feet.  To help understand how high that is, the average wooden telephone pole sticks out of the ground 30-40 feet high.  So the tsunami was as high as two wooden telephone poles.