It is rarely possible to measure the winds around a tornado directly, so its strength is assessed by a mixture of its size and the damage it causes. There are currently two methods in use. In America, the Fujita or F-scale has been developed. This has a range from F0 to F5, with F5 being the most powerful and destructive.
| Fujita intensity |
Description of tornado and wind speeds |
Description of damage
(for guidance only) |
| F0 |
Light damage (<73 mph) |
Some damage to chimneys; branches broken off trees; shallow-rooted trees pushed over; sign boards damaged. |
| F1 |
Moderate damage (73-112 mph) |
Peels surface off roofs; mobile homes pushed off foundations or overturned; moving autos blown off road. |
| F2 |
Considerable damage (113-157 mph) |
Roofs torn off frame houses; mobile homes demolished; boxcars overturned; large trees snapped or uprooted; light-object missiles generated; cars lifted off ground. |
| F3 |
Severe damage (158-206 mph) |
Roofs and some walls torn off well-constructed houses, trains overturned; most trees in forest uprooted; heavy cars lifted off ground and thrown. |
| F4 |
Devastating damage (207-260 mph) |
Well-constructed houses levelled; structure with weak foundations blown off some distance; cars thrown and large missiles generated. |
| F5 |
Incredible damage (261-318 mph) |
Strong frame houses lifted off foundations and swept away; automobile-sized missiles fly through the air in excess of 100 m; trees debarked; incredible phenomena will occur |
In the UK, a scale based on the Beaufort wind scale is used, which is known as the TORRO or T-scale. This has a range from T0 to T10. As an example the 2005 Birmingham tornado was measured as T3-T4.
| TORRO intensity |
Description of tornado & wind speeds |
Description of damage
(for guidance only)
|
| T0 |
Light tornado 17-24 m/s (39-54 mph) |
Loose light litter raised from ground level in spirals. Tents, marquees seriously disturbed; most exposed tiles, slates on roofs dislodged. Twigs snapped; trail visible through crops. |
| T1 |
Mild tornado 25-32 m/s (55-72 mph) |
Deckchairs, small plants, heavy litter becomes airborne; minor damage to sheds. More serious dislodging of tiles, slates, chimney pots. Wooden fences flattened. Slight damage to hedges and trees. |
| T2 |
Moderate tornado 33-41 m/s (73-92 mph) |
Heavy mobile homes displaced, light caravans blown over, garden sheds destroyed, garage roofs torn away, much damage to tiled roofs and chimney stacks. General damage to trees, some big branches twisted or snapped off, small trees uprooted. |
| T3 |
Strong tornado 42-51 m/s (93-114 mph) |
Mobile homes overturned/badly damaged; light caravans destroyed; garages and weak outbuildings destroyed; house roof timbers considerably exposed. Some of the bigger trees snapped or uprooted. |
| T4 |
Severe tornado 52-61 m/s (115-136 mph) |
Motor cars levitated. Mobile homes airborne/destroyed; sheds airborne for considerable distances; entire roofs removed from some houses; roof timbers of stronger brick or stone houses completely exposed; gable ends torn away. Numerous trees uprooted or snapped. |
| T5 |
Intense tornado 62-72 m/s (137-160 mph) |
Heavy motor vehicles levitated; more serious building damage that for T4, yet house walls usually remaining; the oldest, weakest buildings may collapse completely. |
| T6 |
Moderately-devastating tornado 73-83 m/s (161-186 mph) |
Strongly-built houses lose entire roofs and perhaps also a wall; more of the less-strong buildings collapse. |
| T7 |
Strongly-devastating tornado 84-95 m/s (187-212 mph) |
Wooden-frame houses wholly demolished; some walls of stone or brick houses beaten down or collapse; steel-framed warehouse-type constructions may buckle slightly. Locomotives thrown over. Noticeable de-barking of trees by flying debris. |
| T8 |
Severely-devastating tornado 96-107 m/s (213-240 mph) |
Motor cars hurled great distances. Wooden-framed houses and their contents dispersed over long distances; stone or brick houses irreparably damaged; steel-framed buildings buckled. |
| T9 |
Intensely-devastating tornado 108-120 m/s (241-269 mph) |
Many steel-framed buildings badly damaged; locomotives or trains hurled some distances. Complete debarking of any standing tree-trunks |
| T10 |
Super tornado 121-134 m/s (270-299 mph) |
Entire frame houses and similar buildings lifted bodily from foundations and carried some distances. Steel-reinforced concrete buildings may be severely damaged. |
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