Today I went out for a truly short ride. I mapped it afterward at mapmyrun.com. It was about 2.3 miles. I may have walked that last 0.3 miles.
In my inexperience, I am not yet ready to ride across the major street that separates my neighborhood from the next one over, so I got off and walked my bike across. When I got off the bike to cross that street on the way home, I noticed that I had "jelly legs", so I decided to walk until they felt normal again. That got me home.
2.3 miles. That's all? Well, there was a tiny hill...and it was mostly uphill coming back. Funny how many times I've driven that road and never noticed the slope of it. I dropped 39.7 feet in a mile, which admittedly isn't steep, but my legs were feeling it on the way back up. The other loop that I rode last time is about 3.3 miles, but almost entirely flat, a total ascent of only 33.8 feet over a longer distance.