I agree with the 1/2 mile per lap. You can go to http://www.mapmywalk.com/, zoom in and turn the satellite view on and measure it.
I use the track at Clayton HS on the weekends, it is covered in a rubberized cushion material, very gentle on the joints.
If you take the loop and take the path into the woods, it's 9/10ths of a mile. Just a runners answer.