Surfline forecaster Adam Wright replies:

Wave heights are a little tricky. There are so many different ways to look at the size of the wave. If you took two people and had them look at exactly the same wave they would come up with totally different sizes. It's a matter of perspective (along with some ego) that comes up with the mystical number.

I think this is one of the problems that Surfline had to deal with when it first started. Sean, Chris, and the rest of the boys got on the 976-SURF phone recordings and started spilling out wave heights and people got confused and even angry (they still do sometimes) because they have in there minds a picture of what a 5-foot wave should look like, and it wasn't matching up. So to help sort out the confusion we use a pretty simple conversion...

The logic is pretty simple: We measure the face of the wave (because this should be the only area of the wave that surfers are really interested in) and we apply it to the average surfer, 5'7" to 6'0", as he would be riding slightly crouched along the face of the wave.

It breaks down to something like this:

1' = ankle high
2' = knee high
3' = waist high
3'+ = chest high
4' = shoulder high
5' = head high (remember the slight crouch, no one rides waves standing straight up and down)
6' = overhead
10' = double overhead
15' = triple overhead

Now when we pass out of the 15' range it gets even trickier to estimate wave heights. Most people don't really want to ride waves that big... the guys that do are usually used to using the Hawaiian scale of wave heights (which is generally half the face height) but lately with all the big-wave contests, I have noticed a trend in the big wave surfers to refer to the wave face, (hey a 60' wave sounds a lot bigger than a 30' wave even if in reality they are the same size). Generally Surfline will give both and tell you which one is which.

You brought up a good point about the surfability of conditions with similar wave heights based on location, using North Carolina, Tamarack and Hawaii as examples. The biggest differences between these locations is going to be the type of swell, rather than the location. NC gets mostly wind swell (along most of the east coast)... windswell is very gutless and lacks a lot push and generally takes bigger wave heights to produce fun surfable shape. Tamarack (and the West Coast) picks up more longer-period energy, sometimes called groundswell, this packs more punch than windswell and it takes less size to push you along generally make it more fun to ride on smaller days. Hawaii picks up a lot of groundswell and has very deep offshore water that helps to focus the incoming swell energy... it is this focusing effect, called shoaling, that really adds the punch to the Hawaiian surf... essentially making it the best of the three for riding smaller waves. These differences are just compounded further the more size you add.