Tornado intensity is not measured directly. Wind speeds inside a tornado are almost never recorded by instruments, so the National Weather Service rates each one after the fact by surveying what it destroyed. That damage survey produces an Enhanced Fujita (EF) rating — an estimate of the wind needed to cause the observed damage.
The Enhanced Fujita scale
| Rating | Estimated winds | Typical damage |
|---|---|---|
| EF0 | 65–85 mph | Branches broken, shingles peeled, sign boards damaged. |
| EF1 | 86–110 mph | Roof surfaces stripped, mobile homes overturned, windows broken. |
| EF2 | 111–135 mph | Roofs torn from well-built houses, large trees snapped, cars lifted. |
| EF3 | 136–165 mph | Storeys destroyed in well-built homes, trains overturned, heavy cars thrown. |
| EF4 | 166–200 mph | Well-built houses levelled, structures with weak foundations blown away. |
| EF5 | Over 200 mph | Strong frame houses swept from foundations, steel-reinforced structures badly damaged. |
Why old tornadoes are rated F and newer ones EF
Tornadoes before February 2007 carry F ratings from the original Fujita scale; everything after carries EF ratings. The two are not interchangeable — the EF scale ties each wind estimate to specific damage indicators, which generally lowered the wind speeds assigned to the most violent tornadoes. Throughout this archive both appear exactly as recorded, never converted.
What “violent” means
EF4 and EF5 tornadoes are classed as violent. They make up well under one percent of all tornadoes but cause the majority of tornado deaths. Our complete F5 and EF5 list shows every one mapped in the United States since 1950.