Force	Description	Speed  (kmh)	Specification (inland)
0	Calm	less than 2	Smoke rises vertically
1	Light air	2 - 6	Direction of wind shown by smoke drift
2	Light breeze	7 - 11	Wind felt on face; leaves rustle
3	Gentle breeze	12 - 18	Leaves and small twigs in constant motion
4	Moderate breeze	19 - 30	Dust and loose paper raised, small branches are moved
5	Fresh breeze	31 - 39	Small trees in leaf begin to sway
6	Strong breeze	40 - 50	Large branches in motion
7	Near gale	51 - 61	Whole trees in motion; inconvenient to walk against wind
8	Gale	62 - 74	Twigs broken off trees; progress generally impeded
9	Strong gale	75 - 87	Slight structural damage occurs (slates, tiles removed)
10	Storm	88 - 102	Rare; trees uprooted; considerable structural damage
11	Violent storm	103 - 117	Very rare; accompanied by widespread damage
12	Hurricane	118 or more	Extremely rare; devastation

Force	Description	Speed  (knots)	Specification (at sea)	Waves (m)
0	Calm	less than 1	Sea like a mirror	0.0
1	Light air	1 - 3	Ripples like scales but without foam crests	0.1
2	Light breeze	4 - 6	Small wavelets with glassy, unbroken crests	0.2
3	Gentle breeze	7 - 10	Large wavelets; crests begin to break, glassy foam	0.6
4	Moderate breeze	11 - 16	Large waves start to form; white foam crests; possible spray	1.0
5	Fresh breeze	17 - 21	Moderate longer waves; many white horses, some spray	2.0
6	Strong breeze	22 - 27	Large longer waves; many white crests; probable spray	3.0
7	Near gale	28 - 33	Sea heaps up; foam from breaking crests blown in streaks	4.0
8	Gale	34 - 40	Moderately high longer waves; spindrift; foam streaks	5.5
9	Strong gale	41 - 47	High waves; dense foam streaks, crests topple; spray	7.0
10	Storm	48 - 55	Very high waves; long overhanging crests; sea tumbling, white	9.0
11	Violent storm	56 - 63	Extremely high waves; crests blown to froth, patches of foam	11.5
12	Hurricane	64 or more	Air filled with foam and spray; sea white; driving spray	14.0 +