In 1806 Admiral F. Beaufort invented and introduced a scale used to estimate the force of the wind on the basis of the effects that it has on the sea surface and the sailing ships. The Beaufort Scale is easy to learn and is still in use nowadays. Without any measuring instruments and only by observing the nature one may quickly and quite accurately determine the wind speed

The Beaufort Scale is used to empirically determine the wind intensity. The determination is based chiefly on the observation of the state of the sea and the wave types or objects located on the land; no measuring instruments are used.

Beaufort wind scale

°B	Description	For use on land	For use at sea	Wind km/h	Wind Mm/h	Wave length [m]*	Wave height [m]*
0	Calm	Smoke rises vertically.	Sea like a mirror.	0-1	0-1	-	-
1	Light air	Direction of wind shown by smoke drift but not by wind vanes.	Ripples with the appearance of scales are formed, but without foam crests.	2-6	1-3	to 5	0.1-0.2
2	Light breeze	Wind felt on face, leaves rustle, ordinary wind vanes moved by wind.	Small wavelets, still short but more pronounced. Crests have a glassy appearance and do not break.	7-12	4-6	to 15	0.2-0.3
3	Gentle breeze	Leaves and small twigs in constant motion, wind extends light flags.	Large wavelets. Crests begin to break. Foam of glassy appearance. Perhaps scattered white horses.	13-18	7-10	to 25	0.6-1.0
4	Moderate breeze	Wind raises dust and loose paper, small branches move.	Small waves, becoming longer, fairly frequent white horses.	19-26	11-16	to 50	1.0-1.5
5	Fresh breeze	Small trees in leaf start to sway, crested wavelets on inland waters.	Moderate waves, taking a more pronounced form, many white horses are formed. Chance of some spray.	27-35	17-21	to 75	2.0-2.5
6	Strong breeze	Large branches in motion, whistling in telegraph wires, umbrellas used with difficulty.	Large waves begin to form, the white foam crests are more extensive everywhere. Probably some spray.	36-44	22-27	to 100	3.0-4.0
7	Near gale	Whole trees in motion, inconvenient to walk against the wind.	Sea heaps up and white foam from breaking waves begins to be blown in streaks along the direction of the wind.	45-54	28-33	to 135	4.0-5.5
8	Gale	Twigs break from trees, difficult to walk.	Moderately high waves of greater length; edges of crests begin to break into spindrift. The foam is blown in well marked streaks along the direction of the wind.	55-65	34-40	150-200	5.5-7.5
9	Strong gale	Slight structural damage occurs, chimney pots and slates removed.	High waves. Dense streaks of foam along the direction of the wind. Crests of waves begin to topple, tumble and roll over. Spray may affect visibility.	66-77	41-47	150-200	7.0-10.0
10	Storm	Trees uprooted, considerable structural damage occurs.	Very high waves with long over hanging crests. The resulting foam in great patches is blown in dense white streaks along the direction of the wind. On the whole, the surface of the sea takes on a white appearance. The "tumbling" of the sea becomes heavy and shock-like. Visibility affected.	78-90	48-55	to 250	9.0-12.5
11	Violent storm	Widespread damage.	Exceptionally high waves (small and medium sized ships might be lost for a time behind the waves). The sea is completely covered with long white patches of foam lying along the direction of the wind. Everywhere, the edges of the waves are blown into froth. Visibility affected.	91-104	56-63	to 300	11.5-14.0
12	Hurricane	Widespread damage.	The air is filled with foam and spray. The sea completely white with driving spray, visibility very seriously affected.	over 104	over 63	and longer	15.0 and higher

* One should treat given lengths and heights of waves as average values

Douglas Sea Scale

	Height [m] h1/3*	State of the sea
0	0	Calm sea
1	to 0,1	Sea rippled
2	0,1 - 0,5	Smooth
3	0,5 - 1,25	Slight
4	1,25 - 2,5	Moderate
5	2,5 - 4,0	Rough
6	4,0 - 6,0	Very rough
7	6,0 - 9,0	High
8	9,0 - 14,0	Very high
9	over 14,0	Phenomenal

* significant