If you're still trying to figure out width, here's what did it for me (totally unscientific test here):
My hair LOOKS big, because it's curly. People have always called it "thick" - so I assumed the hair itself was thick.
Then I noticed whenever I put it in a ponytail or braid, it completely disappeared down to a tiny baby braid. It looked just like when people put a little kid's hair in a band, it's like the thickness of your pinky finger. My hair does that, despite taking up a lot of space when it is loose. And yes, I get the "pony poof" if I'm not careful.
This is basically how I learned the difference between width (my hairs themselves are fine) and density (I have about a hundred million billion hairs). I've learned to like that combo now that I know what it means, but it was awful when I thought my hair was "thick" and tried to style it as if it were or use products for "thick unruly hair."
For references, I have dark brown/auburn hair, but one dry hair held up to the light is like a wisp. When my hair is wet, a single one becomes much darker and easier to see.
I sort of blog
I'm mostly away doing field work through mid-May.
Hair: curlybob, fine, dense, low-po, big waves/ringlets (2C/3A)
Co-Wash: Nature's Gate Herbal Conditioner
RO: YTC Carrot, Aubrey Organics GPB
LI: BS Shea Soft Styling Cream (HG)
Styling: KCCC, Garnier P&C Gel
1xWeek: low-poo, gelatin PT or Joico K-Pak
Hair Likes: aloe, coconut oil, humidity, protein, long walks on the beach