Land records · Parcel maps · October 6, 2026
What Is NAVD 88? The Vertical Datum for Elevations
What is NAVD 88? The North American Vertical Datum of 1988, the zero point for most U.S. elevations on surveys, flood maps, and elevation certificates.
What is NAVD 88? NAVD 88 stands for the North American Vertical Datum of 1988. It is the reference that most U.S. elevations are measured from, so when a survey, flood map, or elevation certificate says a floor is at 52.4 feet, that number usually means 52.4 feet above the NAVD 88 reference surface. It replaced an older datum, NGVD 29, and is itself scheduled to be replaced by a newer system. This page is general land-records background, not legal advice.
Why a datum matters
Elevation always needs a zero point. “Sea level” sounds simple, but sea level varies from place to place and over time. A vertical datum fixes an agreed reference so that elevations from different surveys, agencies, and decades can be compared. Without it, a floor elevation and a flood elevation could be measured from different zeros and give a false answer.
NAVD 88 vs NGVD 29
| Feature | NGVD 29 | NAVD 88 |
|---|---|---|
| Adopted | 1929 | 1991 (named for 1988) |
| Basis | Mean sea level at many tide stations | A single tide station reference with a modern leveling network |
| Use today | Older maps, plans, and records | Most current FEMA maps and surveys |
The difference between the two varies by location, from near zero to several feet. You cannot just subtract a single number nationwide. Agencies publish conversion tools and factors for specific places.
Where you will see NAVD 88
- Flood insurance rate maps list base flood elevations in a stated datum, usually NAVD 88 on newer maps.
- Elevation certificates must state the datum used for building elevations.
- Topographic surveys and site plans note the datum in the legend or notes.
- Benchmark datasheets give elevations in NAVD 88.
Checking the datum on a flood map
Before comparing a building elevation with a base flood elevation, confirm both are in the same datum. Older flood maps may use NGVD 29, while a new survey may use NAVD 88. A mismatch can make a house appear above or below the flood level when it is not. See how to read a FEMA flood map.
The coming replacement
Federal geodesy agencies are moving to a new vertical reference based on a gravity model and satellite positioning, known as the North American-Pacific Geopotential Datum of 2022. Rollout has been gradual. For now, most local records, flood maps, and surveys still use NAVD 88, and transition tools will connect old and new values.
How surveyors get NAVD 88 elevations
Surveyors either level from a benchmark with a published NAVD 88 elevation or use GNSS receivers with a geoid model that converts satellite heights to NAVD 88. See what is a benchmark in surveying.
Bottom line
NAVD 88 is the main U.S. vertical datum, the zero point for most elevations on current surveys, flood maps, and elevation certificates. It replaced NGVD 29, and the difference between them varies by location. Always check that elevations being compared use the same datum. Find county maps and flood layers via the Platbookmapper map.
What is navd88 FAQ
What does NAVD 88 mean on a survey?
It means elevations are measured from the North American Vertical Datum of 1988.
Is NAVD 88 the same as sea level?
Not exactly. It is a fixed reference surface, not local mean sea level, which varies by place and time.
How do I convert NGVD 29 to NAVD 88?
Use an official conversion tool for your location. The difference varies and is not a single national number.
Do FEMA maps use NAVD 88?
Most newer flood maps do. Older maps may use NGVD 29, so check the map notes.
Will NAVD 88 be replaced?
Yes. A newer geopotential datum is being rolled out, with tools to convert between systems.