An EF rating describes the damage a tornado did, not how to react to a warning. Take shelter for any tornado warning, whatever rating a tornado may later receive.
| EF rating | Estimated 3-second gust |
|---|---|
| EF0 | 65 to 85 mph |
| EF1 | 86 to 110 mph |
| EF2 | 111 to 135 mph |
| EF3 | 136 to 165 mph |
| EF4 | 166 to 200 mph |
| EF5 | Over 200 mph |
| EFU | Unknown: no rating assigned |
The ratings
EF0: 65 to 85 mph. EF1: 86 to 110 mph. EF2: 111 to 135 mph. EF3: 136 to 165 mph. EF4: 166 to 200 mph. EF5: over 200 mph. These are three-second gust estimates, according to the National Weather Service. EF5 is the top of the scale, and there is no EF6.
How the EF scale works: how a rating is assigned
Trained NWS personnel survey the damage and match it to one of 28 damage indicators, such as one- or two-family residences, mobile homes, schools or trees. Each indicator has 8 degrees of damage with an expected range of wind speeds. The evaluator judges where in that range the wind most likely was, repeats this for several structures, and the tornado gets the rating for the highest wind speed that occurred within the damage path.
EFU: when a tornado cannot be rated
Every documented tornado is supposed to get an EF rating, but the NWS says that on rare occasions it is impossible to rate a confirmed tornado because there is little to no damage evidence. In that case it is recorded as EF-Unknown, written EFU, with a short narrative explaining why it went unrated. The NWS gives examples: a tornado that crosses ground already wrecked by an earlier tornado, one in a wilderness or high mountain area that is hard to reach, one that spins up and stays over an inland lake with no marine zone, and satellite tornadoes next to a primary tornado, which does get a rating. EFU does not mean the tornado was weak or strong, only that there was nothing to rate it from.
Estimates, not measurements
The NWS stresses that EF winds are estimates that vary with height and exposure. The three-second gust is not the same wind as in standard surface observations, which use a directly measured one-minute speed in open exposures.
The original Fujita scale
The EF scale was revised from the original Fujita (F) scale to better match wind speeds to damage surveys, with an eye to how most structures are designed.
On this site
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Common questions
What is an EF1 tornado?
An EF1 tornado is rated from damage that points to estimated three-second gusts of 86 to 110 mph. The rating is assigned by the National Weather Service after a damage survey, so a tornado is not rated while it is happening.
What is the highest EF rating?
EF5, for estimated three-second gusts over 200 mph. The scale ends there, and there is no EF6.
What does EFU mean for a tornado?
EF-Unknown. The NWS uses it for a confirmed tornado that left little to no damage evidence, for example one over a mountain wilderness, over an inland lake, or across ground an earlier tornado had already destroyed. It does not say how strong the tornado was.
Who gives a tornado its EF rating?
The National Weather Service is the only federal agency with authority to give official EF ratings. Trained NWS staff survey the damage and match it to damage indicators.
Are EF wind speeds measured?
No. They are estimates from damage, given as three-second gusts, which are not the same as the one-minute winds in standard weather observations.
Does a tornado warning mean the tornado will be rated high?
No. The warning says a tornado is occurring or imminent and you should take shelter, whatever rating it later receives. A rating describes the damage after the fact.
Sources
Reviewed by the Storm Incoming editorial team on October 27, 2026. Follow local emergency officials if their instructions differ.