In 1971, T. T. Fujita proposed a wind scale to cover the range from force 12 at the top of the Beaufort scale to Mach 1, the speed of sound in air, in 12 equal steps.1 The equivalent on the Fujita scale or F-scale of any wind speed M (in meters per second) can be found from the equation
In practice, however, only whole numbers are used, and the wind velocity is estimated from the damage caused to structures, observable in the aftermath, in which respect the Fujita scale resembles the Mercalli Scale for earthquake intensity.
In the United States, since 1 February 2007 official estimates of tornado wind speeds have been made using the Enhanced Fujita Scale instead of the Fujita Scale. Enhanced F-Scale estimates are written, for example, "EF4", while an estimate on the Fujita scale would be writtten "F4".
| F Number |
Wind speed | Description | ||
|---|---|---|---|---|
| meters per second |
miles per hour |
knots | ||
| F0 | 18-32 | 40-72 | 35-62 | Light damage. Some damage to chimneys; break branches off trees; push over shallow-rooted trees; damage sign boards. |
| F1 | 33–49 | 73–112 | 63–97 | Moderate damage. The lower limit is the beginning of hurricane wind speed. Peel surface off roofs; mobile homes pushed off foundations or overturned; moving autos pushed off the roads. |
| F2 | 50–69 | 113–157 | 98–136 | Considerable damage. Roofs torn off frame houses, mobile homes demolished; boxcars pushed over; large trees snapped or uprooted; light-object missiles generated. |
| F3 | 70–92 | 158–206 | 137–179 | Severe damage. Roofs and some walls torn off well-constructed houses; trains overturned; most trees in forest uprooted; heavy cars lifted off ground and thrown. |
| F4 | 93–116 | 207–260 | 180–226 | Devastating damage. Well-constructed houses leveled; structure with weak foundation blown off some distance; cars thrown and large missiles generated. |
| F5 | 117–142 | 261–318 | 227–276 | Incredible damage. Strong frame houses lifted off foundations and carried considerable distance to disintegrate; automobile-sized missiles fly through the air in excess of 100 meters; trees debarked; incredible phenomenon will occur. [Steel-reinforced concrete structures damaged.] |
| F6– F12 |
142– Mach 1 |
319–Mach 1 | 277– Mach 1 | Not expected to occur. |
When the Fujita scale is applied to tornadoes, the force numbers have approximately these meanings:
| Force | Description |
|---|---|
| F0 | a gale tornado |
| F1 | a moderate tornado |
| F2 | a significant tornado |
| F3 | a severe tornado |
| F4 | a devastating tornado |
| F5 | an incredible tornado |
© copyright istockphotocom/Clint Spencer
An F3 tornado
Beaufort wind scales
TORRO Hailstorm Intensity Scale
Saffir-Simpson Damage Potential Scale for hurricanes
1. T. T. Fujita.
Tornadoes and downbursts in the context of generalized planetary scales.
Journal of the Atmospheric Sciences, volume 38,
number 8 (August 1981).
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Last revised: 10 May 2008.