WMO Sea State Code

Code Wave Height
(meters)
Wave Height
(feet)
Characteristics
0
0
0
Calm (glassy)
1
0 - 0.1
4"
Calm (rippled)
2
0.1 - 0.5
4 - 20"
Smooth (wavelets)
3
0.5 - 1.25
20" - 4'
Slight
4
1.25 - 2.5
4' - 8'
Moderate
5
2.5 - 4
8' - 13'
Rough
6
4 - 6
13' - 20'
Very rough
7
6 - 9
20' - 30'
High
8
9 - 14
30' - 46'
Very high
9
Over 14
>46'
Phenomenal

http://en.wikipedia.org/wiki/Sea_state

Swell Scale (Douglas)

0 = Calm
Swell Height
Low
Moderate
High
Wave Period
<2m
2-4m
>4m
Short
<100m
1
4
7
Average
100-200m
2
5
8
Long
>200m
3
6
9