Geoid Height Calculator

Estimate the geoid undulation (N) at any latitude/longitude using a simplified EGM96 model, then convert between ellipsoid height (GPS) and orthometric height (elevation above sea level).

Location

−90 (South Pole) to +90 (North Pole)

−180 (west) to +180 (east)

Geoid Undulation (N)

—

meters (EGM96 approximation)

Ellipsoid height (h)

—

meters

Orthometric height (H)

—

meters

Height Relationship

h = H + N

Formula

h = H + N

  • h — ellipsoid height (GPS altitude, WGS-84)
  • H — orthometric height (above mean sea level)
  • N — geoid undulation (this calculator)

Summary

Estimate the geoid undulation (N) at any latitude/longitude using a simplified EGM96 model, then convert between ellipsoid height (GPS) and orthometric height (elevation above sea level).

How it works

  1. Enter a latitude (−90° to 90°) and longitude (−180° to 180°) in decimal degrees.
  2. The calculator looks up the geoid undulation N from a built-in EGM96 approximation grid.
  3. Bilinear interpolation refines N between grid nodes for smoother results.
  4. If you enter an ellipsoid height (from GPS), the tool computes orthometric height H = h − N.
  5. If you enter an orthometric height, it computes the ellipsoid height h = H + N.
  6. Results are shown in meters with a visual summary of the height relationship.

Use cases

  • Convert raw GPS altitude readings to mean-sea-level elevation for mapping.
  • Verify orthometric heights in GIS projects that mix GPS and leveling data.
  • Check geoid undulation before importing drone survey data into engineering software.
  • Understand why GPS elevation differs from a topo map contour value.
  • Provide a quick N estimate for field surveys before accessing a full geoid grid file.
  • Teach geodesy students the ellipsoid–geoid–topography height relationship.

Frequently Asked Questions

Last updated: 2026-06-24 · Reviewed by Nham Vu