Judging Wave Heights
Keep in mind that everyone's wave scale differs a bit. Depending on who you ask, the same wave can be anywhere from 1 foot to 12 foot. Hawaiian wave scale is usually measured from the back of the wave and then cut down a little more. So a chest high wave is said to be 1-2 feet. It varies by area, but most people from the west coast of the US mainland measure waves by the face.
So, with this scale (wave face), you'll get 3-5 feet for a chest high wave. If you ask someone from the east coast or anywhere that doesn't traditionally have consistent swell, they'll say a chest high wave is anywhere from 6 foot to 15 foot.
We've put together an equation to better help understand how a person will judge the size of a wave:
1/[(Level or Experience of Surfer) + (distance from the East Coast) + (Personal sense of machismo)] = Perceived Size of Wave
Should've Been Here Yesterday
Another equation that lends understanding to the psychology of a surfer is the "You Should've Been There Yesterday" scale. With this scale, the wave conditions and size move in the other direction in order to make the receiver jealous. Our equation:
(Actual quality of surf) x (days until surfer is able to surf again) x (distance of next swell window) x (days since last good swell) x (level of dislike of receiver + amount of times surfer has had receive make surf feel jealous in the past) = Quality of Size and Condition of Waves (Includes crowd factor, water temp, and attractive people on the beach afterwards with beers and fresh seafood being BBQ'd)