ForceDescriptionSpeed  (kmh)Specification (inland)
0Calmless than 2Smoke rises vertically
1Light air2 - 6Direction of wind shown by smoke drift
2Light breeze7 - 11Wind felt on face; leaves rustle
3Gentle breeze12 - 18Leaves and small twigs in constant motion
4Moderate breeze19 - 30Dust and loose paper raised, small branches are moved
5Fresh breeze31 - 39Small trees in leaf begin to sway
6Strong breeze40 - 50Large branches in motion
7Near gale51 - 61Whole trees in motion; inconvenient to walk against wind
8Gale62 - 74Twigs broken off trees; progress generally impeded
9Strong gale75 - 87Slight structural damage occurs (slates, tiles removed)
10Storm88 - 102Rare; trees uprooted; considerable structural damage
11Violent storm103 - 117Very rare; accompanied by widespread damage
12Hurricane118 or moreExtremely rare; devastation


ForceDescriptionSpeed  (knots)Specification (at sea)Waves (m)
0Calmless than 1Sea like a mirror0.0
1Light air1 - 3Ripples like scales but without foam crests0.1
2Light breeze4 - 6Small wavelets with glassy, unbroken crests0.2
3Gentle breeze7 - 10Large wavelets; crests begin to break, glassy foam0.6
4Moderate breeze11 - 16Large waves start to form; white foam crests; possible spray1.0
5Fresh breeze17 - 21Moderate longer waves; many white horses, some spray2.0
6Strong breeze22 - 27Large longer waves; many white crests; probable spray3.0
7Near gale28 - 33Sea heaps up; foam from breaking crests blown in streaks4.0
8Gale34 - 40Moderately high longer waves; spindrift; foam streaks5.5
9Strong gale41 - 47High waves; dense foam streaks, crests topple; spray7.0
10Storm48 - 55Very high waves; long overhanging crests; sea tumbling, white9.0
11Violent storm56 - 63Extremely high waves; crests blown to froth, patches of foam11.5
12Hurricane64 or moreAir filled with foam and spray; sea white; driving spray14.0 +