Is there a way to know whether your hair diameter is average, thin or thick? When I was younger I had average hair thickness, but do not know if it was due to density or hair diameter.

I too wish our expectations could be exacted with a precise scientific assessment. Unfortunately, I do not think this is the case.

One's best bet is to go in person for a consultation and get a docs opinion of your hair characteristics. Since each individual hair from your donor area will vary in terms of diameter thickness and mass they will not be able to measure a few random hairs and show you a patient with an exact equal thickness of caliber hair.

That sucks.

I wish it was more as you had described it, but from my understanding this is not realistic. But they will tell you if your hair is: fine, average, or thick in caliber. A long with other characteristics which either play in your favor or to your detriment...