| 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 + |