Calibrating Computer - I Hate Math

I just picked up my first computer. I need to figure out the circumference of my wheel to calibrate it, and It's giving me a bit of trouble. My wheel is 700 x 25.

Here's the formula I followed, as per the manual:

distance from floor to hub: 13 3/8" (13.375)

multiply by 25.4 to convert to mm (339.725)

multiply that number by 6.28 (2 x pi) = 2133.473

I had entered 2105 based on Sheldon Brown's recommendation for a 700 x 25 wheel. But this is a pretty substantial difference. When I entered 2133, it seemed like the miles were racking up really quickly. I'll be the first to admit that I don't have the best sense of distance, so I could be wrong.

Any ideas?