Ellipsoidal to orthometric height converter (GNSS h → H) — EGM2008 geoid
Converts the ellipsoidal height (h) from your GNSS receiver into orthometric height (H) above mean sea level, and back, with the global EGM2008 geoid model. Works anywhere in the world. One point or a whole list pasted from Excel.
Decimal degrees or degrees/minutes/seconds, with or without a point name. Without a height, the calculator shows only the geoid undulation at that spot. You can also click on the map.
Accepts E N h or name E N h, separated by spaces, tabs or semicolons.
Only the latitude and longitude go to our server, to read the geoid model grid (nothing is stored). The height stays on your device.
Result
Type or paste the points above. The result shows up here instantly.
How it works
GNSS measures ellipsoidal height (h), relative to the WGS 84 ellipsoid, a mathematical surface. Maps, designs and benchmarks use orthometric height (H), measured from the geoid, the mean sea level surface extended under the continents. The distance between the two surfaces is the geoid undulation (N), which ranges from about −107 m to +86 m around the planet: H = h − N.
EGM2008 (Earth Gravitational Model 2008, from the US NGA) is the global geoid model used by GNSS receivers and surveying software worldwide. We use the official 5' grid with bilinear interpolation, checked against GeographicLib's reference computation at 25 points around the world: 2.6 cm RMS difference. In Brazil, the calculator automatically switches to the official IBGE model (hgeoHNOR2020).
Note: every country has its own official vertical datum and often its own geoid model, more accurate in that region (GEOID18 in the US, OSGM15 in Great Britain, and so on). EGM2008 gives the height above global mean sea level, which can differ from the official national height by a few centimetres to more than a metre. For official work, tie the survey to a local benchmark.
FAQ
What is the difference between ellipsoidal height, orthometric height and geoid height?
Ellipsoidal height (h) is what GNSS measures, from the WGS 84 ellipsoid. Orthometric height (H) is the "physical" height above mean sea level used on maps and in designs. Geoid height or undulation (N) is the distance between the ellipsoid and the geoid at that spot: H = h − N.
What is EGM2008?
It is the global geoid model published in 2008 by the NGA, the US geospatial-intelligence agency, computed from satellite and terrestrial gravity data. It is the default model in many GNSS receivers and surveying programs, and the global reference for heights above mean sea level.
How accurate is it?
EGM2008 itself is accurate to a few centimetres where good gravity data exist and to a few decimetres in mountains or data-poor regions. Interpolating the 5' grid adds 1 to 3 cm on average. For official work, use your country's geoid model if there is one, and tie in to a benchmark.
Is the result the official height in my country?
Not always. Each country defines its own vertical datum (a tide gauge and a levelling network), and the official height can differ from EGM2008 by a few centimetres to more than a metre (NAVD 88 in the US, for example). EGM2008 is great for checking, planning and working where there is no local model.
Can I convert a whole list?
Yes, up to 1,000 points at a time. Paste from Excel (name, coordinates and height) and download the result as CSV or copy the table back.