Ruler
And here I was with my ruler ready to tell you:
2 inches including the tip
1 7/8 inches without the tip
Not what you were really looking for, though. 😛
I'm sure Apple's numbers use non-rechargeable batteries (the blue ones specially made for electronics). It makes much more sense to use the rechargeables. You'll change them more often (mine go about a month with constant use), but it's worth it.
🙂