The height of a wave is measured from the crest, or top, to the trough, the point where the wave rises from the surface.
A wave’s height depends on the speed of the wind and the length of time the wind blows. The faster and longer the wind blows, the higher the waves will be.
Unless whipped up by storms, mid-ocean waves tend to be moderate, from a few feet to 15 feet (4.6 meters) high. (In the middle of the ocean, 15 feet is not considered big.)
Waves can be minute ripples or they can be tsunamis, taller than trees and buildings.