What Is the Tornado EF Scale Calculator?
The Enhanced Fujita (EF) Scale is the system used in the United States (and adopted in several other countries) to rate tornado intensity based on the damage produced and the estimated 3-second peak gust wind speed. This calculator takes that estimated gust speed and tells you which EF category — from EF0 (weak) to EF5 (catastrophic) — the tornado falls into. It replaced the original Fujita (F) Scale in 2007 to better align wind-speed estimates with observed damage.
How to Use It
Enter the estimated 3-second gust wind speed and choose your unit (mph or km/h). The calculator converts km/h to mph if needed, then matches the speed against the official EF thresholds and returns the rating, the EF number, and the equivalent gust speed in mph.
The Formula Explained
The EF Scale uses fixed wind-speed bands measured as a 3-second gust: EF0 is 65–85 mph, EF1 is 86–110 mph, EF2 is 111–135 mph, EF3 is 136–165 mph, EF4 is 166–200 mph, and EF5 is any gust over 200 mph. Speeds below 65 mph are not classified as a tornado on this scale. Because these are damage-indicator estimates, a real-world rating is also adjusted by trained surveyors examining structural damage.
$$\text{EF} = \begin{cases} \text{Below EF0} & V < 65 \\ \text{EF0} & 65 \le V \le 85 \\ \text{EF1} & 85 < V \le 110 \\ \text{EF2} & 110 < V \le 135 \\ \text{EF3} & 135 < V \le 165 \\ \text{EF4} & 165 < V \le 200 \\ \text{EF5} & V > 200 \end{cases} \qquad V = \text{Wind Speed (mph)}$$
Worked Example
Suppose a tornado produces an estimated 3-second gust of 150 mph. That value falls in the 136–165 mph band, so the tornado is rated EF3 — a strong tornado capable of severe damage, including leveling well-constructed houses and uprooting trees. A 250 km/h gust converts to about 155.3 mph, which is also EF3.
$$\frac{250}{1.609344} \approx 155.3 \text{ mph}$$FAQ
Is the EF Scale based on wind speed or damage? Both. Surveyors assess damage indicators, then assign the EF rating tied to the estimated wind speed that caused that damage.
What is the strongest possible rating? EF5, for gusts over 200 mph — these are extremely rare and devastating.
Does this apply worldwide? The EF Scale is the official standard in the US and Canada; other countries may use the original Fujita Scale or the international IF Scale, though the wind bands are similar.
