Base flood elevation (BFE)

Checked against FEMA and other official sources · Last reviewed October 8, 2026

What base flood elevation means

FEMA defines the BFE as "the computed elevation to which floodwater is anticipated to rise during the base (1-percent-annual-chance) flood event." FloodSmart, the NFIP's official site, calls it "the elevation of surface water resulting from a flood that has a 1% chance of equaling or exceeding that level in any given year." Federal regulations define the base flood the same way: "the flood having a one percent chance of being equalled or exceeded in any given year." FEMA also calls this the "base, or 100-year, flood." See what a 100-year flood means.

A BFE is an elevation, not a depth. FEMA's flood map course says the map label gives the water surface elevation of the base flood "in relation to a standard set of geographic data." That reference is the vertical datum. Two datums are common on flood maps:

• NGVD 29, the National Geodetic Vertical Datum of 1929. FloodSmart says it was "formerly referred to as Mean Sea Level (MSL) of 1929" and "may be used as the reference datum on some Flood Insurance Rate Maps."
• NAVD 88, the North American Vertical Datum of 1988. FloodSmart says it "replaces the National Geodetic Vertical Datum (NGVD) of 1929."

So a BFE of 110 does not mean 110 feet of water. It means the water surface would reach 110 feet above the map's datum. To know how deep the water would be at your house, you compare the BFE with your ground or floor elevation measured on the same datum. FEMA's elevation certificate instructions say the vertical datum "is shown in the Map Legend and/or the Notes to Users on the FIRM," and that all elevations on the certificate "must use the same datum on which the BFE is based." [1][2][3][4][7][8]

Which flood zones have a BFE

FEMA's elevation certificate instructions say BFEs "are shown in the FIS or on a FIRM" for these zones:

• AE and A1-A30: high-risk areas "with water surface elevations determined." See flood zone AE.
• AH: shallow flooding of 1 to 3 feet, "with water surface elevations determined." See flood zone AH.
• VE and V1-V30: coastal high hazard areas with water surface elevations determined. See flood zone VE.
• AR zones: AR, AR/A, AR/AE, AR/A1-A30 and AR/AH.

Some high-risk zones have no BFE on the map:

• Zone A is defined as a special flood hazard area "without water surface elevations determined." See flood zone A.
• Zone V is the coastal version, also "without water surface elevations determined." FEMA's map course says zone A and zone V areas without BFEs "were determined by less than detailed study methods."
• Zone AO shows a base flood depth instead of an elevation. The elevation certificate instructions say "base flood depths are shown for Zones AO and AR/AO." See flood zone AO.

Zones B, C, X and D are not on FloodSmart's list of zones with a BFE. B and shaded X are moderate-risk areas, C and unshaded X are minimal-risk areas, and D is an area of undetermined but possible flood hazard. See FEMA flood zones explained. [2][3][4][9]

How BFEs appear on flood maps and in flood studies

FEMA's flood map course describes two ways a BFE is shown on a Flood Insurance Rate Map (FIRM):

• A wavy line with a number. "A wavy line is used to indicate when this rounded base flood elevation varies along a watercourse." This is typical along rivers in AE zones.
• A label under the zone name. "When the rounded base flood elevation is uniform across a large area, a BFE label below the zone label is used." This is typical in ponding AH zones, lake AE zones and coastal AE and VE zones.

The map number is rounded. FEMA says BFEs for rivers and other non-coastal waters shown on the map "are rounded to the nearest foot," so they "are only accurate to plus or minus 6 inches." The course adds: "you must refer to the Flood Insurance Study Profile to get the actual BFE for floodplain management and flood insurance purposes."

The Flood Insurance Study (FIS) report has the more exact numbers. For an accurate BFE, FEMA says floodplain professionals "must use the riverine Flood Profiles, or Stillwater Data Tables" in the FIS. The elevation certificate asks for the BFE "to the nearest tenth of a foot," taken from the FIS profile, an FIS data table or the FIRM panel.

For a rough estimate along a river, FEMA's course suggests using the BFE line just upstream of the property and adding half a foot. In its example, line 110 near the upstream corner gives a conservative estimate of 110.5. [3][4]

How to find the BFE for your property

1. Look up your map. FEMA's Map Service Center (msc.fema.gov) is "the official public source for flood map." Search your address, then check your zone and any BFE line or label near your building. Our guide to finding your flood zone walks through it.
2. Get the Flood Insurance Study. FEMA's course says the FIS, preliminary maps, historic map panels and Letters of Map Change can be found with the Map Service Center's "Search All Products" option.
3. Ask your local floodplain manager. The elevation certificate instructions say to "visit msc.fema.gov or contact the local floodplain management official to access the current FIS and FIRM." Some FIRM indexes also list a map repository address: the official community office where copies of the flood map and FIS report "are made available to the public."
4. Check for an existing elevation certificate. An elevation certificate lists the BFE and its source in Section B, and your building's surveyed elevations in Section C.

If your zone has no BFE, FEMA says possible sources include the community's floodplain administrator, planning, public works or engineering departments, the local U.S. Army Corps of Engineers district, and state agencies such as the State NFIP Coordinating Office. A registered professional engineer "could conduct an engineering analysis to determine the BFE at the site." Communities must require BFE data for zone A subdivisions and developments "greater than 50 lots or 5 acres, whichever is the lesser."

Your area may also have newer flood data that is not yet on the effective map. The elevation certificate instructions mention "best available data, such as base-level engineering or advisory flood hazard data" and say to "contact the local floodplain management official to confirm." [1][3][4][5]

How the BFE sets building rules

Communities in the National Flood Insurance Program (NFIP) must enforce minimum building standards, and most are measured from the BFE:

• Zones AE, A1-A30 and AH (homes): new construction and substantial improvements must have "the lowest floor (including basement) elevated to or above the base flood level." Limited basement exceptions exist only where FEMA has granted one to the community.
• Zones AE, A1-A30 and AH (non-residential buildings): the lowest floor must be at or above the base flood level, or the building must be floodproofed so that "below the base flood level the structure is watertight."
• Zones VE, V1-V30, and zone V where BFE data are available: buildings must be elevated on pilings or columns so that "the bottom of the lowest horizontal structural member of the lowest floor (excluding the pilings or columns) is elevated to or above the base flood level."
• Zone AO: there is no BFE, so the rule uses the depth number. Homes must have the lowest floor "elevated above the highest adjacent grade at least as high as the depth number specified in feet on the community's FIRM (at least two feet if no depth number is specified)."
• Zone A: the community must "obtain, review and reasonably utilize" BFE data from federal, state or other sources and apply the elevation standards where such data exist.

Communities must record the elevation of the lowest floor of new and substantially improved buildings "in relation to mean sea level." In V zones, they record the elevation of the bottom of the lowest structural member.

These are minimums. Federal rules say the criteria are "minimum standards" and "any community may exceed the minimum criteria." One common higher standard is freeboard. FloodSmart defines it as "an additional amount of height above the Base Flood Elevation used as a factor of safety (e.g., 2 feet above the Base Flood)." The elevation certificate has a line for the community's minimum elevation, "including freeboard above the BFE." Ask your floodplain manager what height your community requires before you build, add on or repair major damage. [2][4][5][10]

How the BFE affects flood insurance

FloodSmart says that under the NFIP's current pricing approach, "flood zones and the structure's elevation relative to Base Flood Elevation (BFE) – as depicted on flood maps - are no longer the only factors utilized in setting flood insurance premiums."

FEMA says the NFIP's pricing approach "does not use flood zones to determine flood risk." It uses factors such as flood frequency, several flood types, and "distance to a water source along with property characteristics such as elevation and the cost to rebuild."

An elevation certificate shows "the height of its lowest floor compared to the Base Flood Level (BFE)," in FloodSmart's words. You don't need one to buy NFIP coverage. FloodSmart says an EC "is not required to purchase coverage," and that FEMA instead uses a building's first floor height as one rating factor. FloodSmart says property owners "can choose to submit an EC to their agent to see if it will lower their insurance costs." Ask your agent whether an EC would change your quote. See flood insurance cost.

The BFE also matters for map changes. FEMA's map course says that if the lowest ground at your property or next to your building is below the BFE, the property or building "is confirmed as in the SFHA." If the map shows it in the SFHA by mistake, or it was raised above the BFE with fill, you can apply for a Letter of Map Amendment (LOMA) or a Letter of Map Revision based on Fill (LOMR-F). [3][6][11][12]

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