Exactly, I did a test with an ex-girlfriend of mine years ago, where I said I was as long as a half liter can of beer but she thought I was smaller than that.
Damn was she surprised when I whipped it out and showed her I was correct. Nowadays though I will use a can of Gillette shaving cream which is exactly 7,5 inches, or 19 cm long to show I’m actually longer than that.
Sometimes women needs a point of reference to compare with as I did with the tall can of beer.