While flying having trouble estimating how far I am from Airport When approaching an uncontrolled airport especially, standard procedure demands to make the first call 10 miles out announcing my location, entry procedure, etc. and then more calls at 5 miles, 2 miles, etc. I find myself having a hard time estimating how far I am from an airport so I can announce my position. The same applies when I'm asked to report a 8 mile final in a controlled airport. I'm curious how others do it and if there's a more reliable way to judge distance from an airport. Thanks.
My GPS tells me the distance. 

Otherwise, my experience says:


15 miles (and about 3,000 AGL) is where I'm not entirely sure I have the airport picked out.
10 miles is where I can see the airport, but not pick out specific details and airplanes.
5 miles is where I can see the airport clearly, and setup for the centerline.