How is my Flood Factor calculated?

Learn about the data used to calculate a property’s Flood Factor. 


Property Flood Factors 

A property's Flood Factor is not only a score ranging from 1-10, it is a comprehensive risk assessment including a property's thirty-year risk of flooding from high intensity rainfall, overflowing rivers and streams, high tides, and storm surge. Properties with higher Flood Factors are either more likely to flood, more likely to experience high floods, or both.

Please note that at this time, personal protections such as a drainage system, sump pump, sealed or elevated homes in addition to the building's elevation are not taken into account in the Flood Factor's calculation. Flood Factors are indicators of water reaching the building footprint, not the interior of the home.



Calculation of Flood Factor rankings

That data on Flood Factor comes from the First Street Foundation Flood Model, a nationwide flood model that calculates the likelihood of a flood based on a location’s history and geographic information, such as elevation, climate, changes in the environment, proximity to water, and adaptation measures. 

A property’s Flood Factor is determined by its likelihood of flooding and the potential depth of that flood. Because flood risks accumulate over time, it specifically looks at the likelihood of 1 inch of water reaching the largest home or building on a property at least once within the next 30 years. 

The First Street Foundation Flood Model is used to determine the likelihood of a flood occurring within a given year and the projected depth of a flood. Flood Factor ranks increase as the 30-year cumulative flood likelihood increases, or as the projected depth of flooding increases. Properties with a less than 0.2% chance of flood water reaching the building in every year analyzed are considered to have minimal risk or a Flood Factor of 1. While it is still possible for properties with a Flood Factor of 1 to flood, they are not included in the Flood Factor matrix.


Please note that only FEMA maps are used to determine flood insurance and building code requirements, not Flood Factor scores. Additionally, FEMA zone designations are not a factor in calculations used to determine a Flood Factor. 

Flood Factor Matrix


Properties more likely to experience a flood with a greater depth have higher Flood Factors. 

For example, a property with an 8% chance of flooding 16 inches at least once within 30 years would have a Major Flood Factor of 5. A property with more than a 96% chance of any depth of flooding would have a Flood Factor of 7 or greater.

Ensuring scientific accuracy

The creation of the First Street Foundation Flood Model required an unprecedented partnership of more than 80 world-renowned scientists, technologists and analysts. Methods used in the Flood Model have undergone an expert academic panel review and have been submitted to scientific peer-review journals. Where possible, data has been validated against historic flood reports and FEMA flood claims.The data the model produces undergoes multiple reviews and must pass comprehensive check-points before being made publicly available.


Learn more

The data behind Flood Factor

Share information that could impact your property’s Flood Factor Score

What are probabilities and how do they affect my Flood Factor?


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