NGVD 29 to NAVD 88 Conversion Factor

If you don't actually have a benchmark with both NAVD88 and NGVD29, the NGS VDatum Tool is what you are looking for.

Look at NGS Data Sheets for nearby marks to compare the conversions used on those marks:

https://geodesy.noaa.gov/NGSDataExplorer/

VERTCON from FEMA or USGS. FYI in most of Central Florida the elevation difference between the two is 0.92' ?????ÿ

Edit: Beware of the "City of Orlando" their vertical datum used to be in its own world.

@flga-2-2

I'm guessing that world's name started with a D?

Our difference is very close to 0.42 feet in my area of work.

2.45 up to 88 down to 29

29 -0.4 to 88 -1.8 to NSRS

Most recent project;

88 to 29 down 4.40 feet, but varies about 0.1 across the [SMALL] project.

Depends on where you are...

There is no ƒ??accurate ƒ?? conversion, unless you might want it good to 0.1 feet in a low elevation flat region of land.

LOL to those who gave the adjustment in their area! They are all different! The difference between the datums is relative to where in the country you are.?ÿ

@geeoddmike

Dang.?ÿ The use of longitude east through there for a bit.?ÿ It's bad enough needing to convert from smoots to U.S. Feet.

With respect to references to non-NGS sources of VERTCON, be advised that they probably use version VERTCON 2.1.

This version has been superceded with VERTCON 3.0 which is incorporated into NCAT available at the NGS site.

For those interested in this new version see the Technical Report available here: https://geodesy.noaa.gov/library/pdfs/NOAA_TR_NOS_NGS_0068.pdf#page94

Thanks to all for the abundance of information!

@robertusa

Not sure what you mean "there is no accurate conversion".

The conversion a fixed number depending on location.