Hawaiian scale is an expression of the height of a wind wave affecting water. It is the expression conventionally used by surfers in Hawaii and is also used in Australia and parts of South Africa.

The expression, always given in feet, is a scaled figure corresponding to roughly half the actual measured or estimated height of a wave's face (trough to crest height). Thus, a "3-foot" wave is roughly six feet high (in actuality a height of ~1.8 m), i.e., head-high to a 6-foot (~180 cm) person; a "2-foot" wave is roughly four feet high (height of ~1.2 m), i.e., chest-high to such a person; and a "6- to 8-foot" wave would be 2 to approaching 3 times head-high to such a person (height of ~3.5 to 5 m). As wave height increases, however, so does the difficulty of judging that height, and as wave height approaches 20 feet (40 ft faces or 12 m height), the range of absolute wave heights corresponding to a given scaled expression tends to widen.
Given this reference text about the Hawaiian scale, how tall is a wave that is six foot Hawaiian?
A wave that is six foot Hawaiian would be twelve feet tall from crest to trough