When measuring antenna height do I go by the base or top of antenna?
The reason I ask  is for bragging rights , some of my friends have 7 foot, 10 foot, or 17 foot tall antennas.
And if we go by tip if antenna the taller antennas have me beat.
My antenna by the way is going to be 10 ft tall on top of  a mast that is 38 feet tall.
It's a comet GP-6 antenna.
So I'm around 48 feet off the ground if I go by tip of antenna.
But how do you guys (the pros) measure the height of your antenna?

Here's just a picture of my mast and mount with no antenna mounted yet.
I am using 1 inch galvanized plumbers pipe because it is so thick and has hardly any flex.
We used this same pipe for flag poles years ago and it work great.  I plan on not needing any guy wires as of right now.
I'm using 3/16 angle iron for the supports and mounts to hold the mast piping.










The braces are strapped and bolted to the chimney at several places.
I have one brace not mounted yet, however it is below in a picture being painted.











The last brace to be mounted to the chimney for extra support.

How high is the mounting point of a ground mounted vertical?  
Use that same reference when you put it up higher.  

Generally you'd refer to the base of the antenna, whatever height it's mounted at.

For calculations for signal propagation or efficiency you'd want the center of radiation, so approximately the middle of the radiating element(s) for a collinear type vertical. Let's say you have a collinear type vertical with 8 feet of active elements.  You replace that with one with 16 feet of active elements, how much height have you gained?  Four feet... center of antenna #1 is 4 feet up, center of antenna #2 is eight feet up.

This is excellent info, thanks for letting me know how to figure out why I wanted to know.