Yes, and the last part of the thumb is roughly an inch. Mine is 1.25 inches almost precisely, and between my feet (almost precisely a foot with most shoes on), and my thumb, I can do rough-and-ready measurements anywhere!
The spread of my hand, with fingers outstretched, is about 8.5” fingertip-to-fingertip. I recently was furniture shopping and I measured a table using my hand as a reference. The young sales clerk was astonished. He said he had never seen anyone measure that way. I told him I had my hand with me always and so could run up a quick “ballpark” measurement whenever I needed.
Younguns!