Associate Editor

One man’s forty feet is another man’s twelve. Measuring wave height in surfing is rife with inconsistency. Photo: Brad Masters

The Inertia

Determining the height of any given wave in space sounds straightforward enough… in theory. After all, a wave measured from trough to crest just before it breaks stands a certain number of feet and inches (or meters, if you prefer) tall, right? What complicates matters is that waves are constantly in motion and that in most cases when surfers assess wave height, they want to know not what the size of that wave was, but what the average height of waves coming through is.

As it happens, surfers have had a tenuous relationship with the height of waves from the beginning. Whether playing down wave height as in Hawaii (a three-foot wave would likely be a six-foot wave in California), or ascribing to a “measure from the back instead of the front” mentality, the average surfer’s assessment of wave height is anything but scientific.

To explain some of the history and nuance, we reached out to knower of all things surf Matt Warshaw who was kind enough to send over an excerpt from his book, the Encyclopedia of Surfing, that investigates the issue of wave height in detail:

“As a matter of science, wave height is defined as the average distance between the trough and the crest of all open-ocean waves that pass by a stationary point over a given period of time – one hour for many Internet reports, for example. Open-ocean wave height is a primary indicator for surf size.


“Nearly as important is wave ‘period’ or ‘interval,’ roughly defined as the average amount of time between successive waves. Given equal wave height, a longer period translates into bigger surf. For example, an incoming swell with eight-foot wave height and a 20-second period might produce 10- to 15-foot surf; while an eight-foot 12-second swell, in contrast, might produce six-foot surf. There has traditionally been a gap between the actual trough-to-crest height of a breaking wave and the height as measured by surfers.

“In the early decades of the 20th century, surfers generally over-estimated wave height. Southern California surfer George ‘Peanuts’ Larson caught and rode a wave at a break called Church in 1939 that he later claimed to be 30 or 40 feet. Given that Larson was riding a finless wooden surfboard, that a photograph of the second-biggest ridden wave of the period (also surfed by him) shows a swell measuring about 12 feet from trough to crest, and that nobody has ever seen or photographed a wave measuring more than 15 feet at Church, Larson’s estimate – accepted as gospel by surfers in the ’40s and ’50s—can be taken as a magnificent exaggeration.

“Underestimating wave size got started in the late 1950s on the North Shore of Oahu, and the practice was widespread by the early ’70s. While the degree of underestimation changes from area to area—in America, the differentiation is less on the East Coast, more pronounced on the West Coast, and greatest in Hawaii – surfers, in general, will judge a wave’s size at about three-fifths of its true linear height. A wave measuring 10 foot from trough to crest, in other words, will be identified as six foot.

“Underestimating wave height may have originated from surfers trying to get a closer match between the breaking wave and its height as an open-ocean swell. Measuring from the back side of the wave, instead of the front (or ‘face’), so the old argument goes, gives a more accurate gauge of ‘real’ wave height. Underestimation can also be viewed as a form of gamesmanship; the surfer offhandedly describing a 10-foot wave as six foot can look cool and superior.

“In what may be the sport’s single most flagrantly underestimated wave, Hawaiian surfer Ken Bradshaw was towed into a monster called Outside Log Cabins, on the North Shore of Oahu, that he at first labeled 35 feet. Video footage of the wave shows that it measured more than 60 feet from trough to crest. (For small and medium-sized waves, surfers will often ignore numeric measurement altogether and instead use a body-height scale: waves are said to be waist-high, shoulder-high, or head-high, or double-overhead. Giant waves, as the old big-wave-riding adage goes, sidestepping the height issue entirely, are measured not in feet but in ‘increments of fear.’)

“California surf journalist Sam George has long been the sport’s most vocal proponent of accuracy in measurement. ‘A wave’s height, like that of a palm tree or an NBA center, is quantifiable,’ he wrote in 1998, signing off with the hope that the surf world would begin to ‘tell it like it is.’

“Big-wave riders themselves continued to undervalue wave size, but judging panels for big-surf photo contests that require contestants submit photographs of themselves riding giant waves, set about making precise trough-to-crest measurements in order to pick a winner. Carlos Burle of Brazil won the 2002 Nissan Xterra XXL Big Surf Awards for a wave measured at 68 foot. Surfers from past generations likely would have called Burle’s wave 35 or 40 feet.”

Be sure to check out the Encyclopedia of Surfing online, and Warshaw’s newest venture the History of Surfing website.

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