The Enhanced Fujita Scale (EF Scale) is the United States rating system that assigns a tornado an intensity from EF0 to EF5 by matching observed damage to standardized indicators and estimating the wind speed most likely to have caused it. It replaced the original Fujita Scale operationally on February 1, 2007.
Why the scale was updated
The original F Scale, introduced by Dr. Ted Fujita in 1971, tied tornado intensity to a small set of damage descriptions. After decades of use, forecasters and engineers converged on three problems. The scale did not name enough damage indicators to be applied consistently. It ignored how much construction quality varies from one building to the next. And at the top of the scale, it appeared to overestimate wind speeds, because the winds needed to level a well-built house are lower than the F5 numbers implied.
Texas Tech University's Wind Science and Engineering Center led a multi-year effort to fix this. Through a formal expert elicitation with meteorologists, engineers, and architects, wind speed ranges were assigned to a much larger and more specific set of damage types.
How the scale works
The EF Scale is expressed in three-second gust wind speeds and is divided into six categories: EF0 at 65 to 85 mph, EF1 at 86 to 110, EF2 at 111 to 135, EF3 at 136 to 165, EF4 at 166 to 200, and EF5 above 200. The rating itself is not a direct measurement of wind. It is an estimate produced by identifying damage indicators along the path, matching each to a degree of damage, and reading off the wind speed that most likely produced that damage under normal construction quality.
Every damage indicator carries an expected value wind speed for each degree of damage, plus a lower and upper bound that lets the surveyor adjust for context. A well-anchored house that failed at a lower speed than expected pushes the estimate down. A poorly built house that failed easily pushes it up. The final rating comes from the strongest well-supported estimate along the path.
How forecasters and researchers use it
The rating becomes the tornado's official intensity in the national storm database. It anchors climatology, verification of watches and warnings, and long-term studies of tornado behavior. It also shapes public messaging, because the EF number carries meaning for viewers who may not track wind speed in miles per hour.
Case-by-case, the rating and the damage path together give researchers what they need to relate a tornado's intensity to the storm's radar and environmental signatures. That connection is what makes tornado climatology and warning verification possible at all.
Important limits
Because the EF Scale is damage-based, its accuracy depends on what the tornado hit. A violent tornado that spends most of its life over open ground can be rated far below its true intensity if it never encounters a well-built structure or a resilient tree stand. Two tornadoes with identical wind speeds can receive different ratings because one crossed a subdivision and the other crossed a field.
The scale is also silent on things it does not measure. Pressure drops, tornado duration, and multi-vortex structure do not appear in the number. The EF rating is a careful engineering estimate of peak wind, and it should always be read as one piece of the event, not the whole story.