The Beaufort Scale For Waves

One of the most common ways for waves to be measured is by the Beaufort Scale.  It was created by Admiral Sir Francis Beaufort of the British Navy in 1805.  It is a measure for what can be expected in certain conditions with an unlimited fetch.  (Fetch is the distance that a wind can travel across the water)

Force	Wind Speed	Description	Sea Conditions	Waves
0	0	Calm	Smooth, like a mirror	0
1	1-3 Knots	Light Air	Small ripples, like fish scales	1/4' - 1/2'
2	4-6 Knots	Light Breeze	Short, small pronounced wavelettes with no crests	1/4' - 1/2'
3	7-10 Knots	Gentle Breeze	Large wavelettes with some crests	2'
4	11-16 Knots	Moderate Breeze	Increasingly larger small waves, some white caps and light foam	4'
5	17-21 Knots	Fresh Breeze	Moderate lengthening waves, with many white caps and some light spray	6'
6	22-27 Knots	Strong Breeze	Large waves, extensive white caps with some spray	10'
7	28-33 Knots	Near Gale	Heaps of waves, with some breakers whose foam is blown downwind in streaks	14'
8	34-40 Knots	Gale	Moderately high waves of increasing length and edges of crests breaking into spindrift (heavy spray). Foam is blown down wind in well-marked streaks.	18'
9	41-47 Knots	Strong Gale	High wind with densefoam streaks and some crests rolling over. Spray reduces visibility.	23'
10	48-55 Knots	Storm	Very high waves with long, overlapping crests. The sea looks white, visibility is greatly reduced and waves tumble with force.	29'
11	56-63 Knots	Violent Storm	Exceptionally high waves that may obscure medium size ships. All wave edges are blown into froth and the sea is covered with patches of foam.	37'
12	64-71 Knots	Hurricane	The air is filled with foam and spray, and the sea is completely white.	45'