It also depends up to an inch or so on how you are standing. With good posture you'll be an inch taller than if you slouch. You can crane your neck probably half an inch beyond that if you try.
The last time I was measured, I had bad posture (because of some awkwardness around how the measuring stand was set up) and the doctor insisted I don't crane my neck (when all I was trying to do was stand up straight and not slouch), so I "lost" an inch compared with every other measurement of my height since I was about 16.
2.5 inches seems like a lot, though, more than you could explain by posture alone.