The measurement of breaking waves along the coast. Surfline measures wave heights by the face of the wave for consistency in communication. When communicating we also compare wave heights to a surfer's body height. Figuring a surfer averages 5 feet tall when semi crouching and surfing a wave: 1 foot = ankle high; 2 feet = knee high; 3 feet = waist high; 4 feet = chest high; 5 feet = head high; 1 foot overhead = 6 feet; 2 feet overhead = 7 feet, etc. ; 10 feet = double overhead; 15 feet = triple overhead, etc. NOTE: Hawaiians and a few other areas throughout the world measure waves by the back of the wave and they estimate the waves backs to be one half of the wave face height. The Hawaiian's intent is probably to stay consistent with the deep-water swell height of the waves before they began to shoal, as compared to the wave heights on Buoy 51001 located NW of Kauai. However, this procedure is inherently flawed because numerous variables like swell period, refraction, and shoaling can greatly alter the transition of deep-water swell to breaking waves by 1. 5 times to 5 times the original deep-water swell height.