Extent is the anticipated severity and/or magnitude of a hazard.

• The best measure or discussion of extent will depend on individual hazards. Measures of strength include depth of flooding, wind speed, peak ground acceleration due to an earthquake, etc.
   
• Use nationally recognized scales when possible to measure a hazard event’s strength (ex: Fujita for Tornadoes, Mercalli for Earthquakes, Saffir-Simpson for Hurricanes, etc.).
   
• Speed of onset is a component of extent because the greater the lead time, the more time there is to prepare and the smaller the potential severity of the extent.
   
• With respect to duration, the longer the duration of an event, the greater the extent. Flooding that peaks and retreats in a matter of hours is typically less damaging than flooding of similar depth that remains in place for days.