Answer:
Sitting down you have it, Standing up you don't.
The distance from the top of your head to the floor standing up straight.
I'm often served as a "rack of ..." I'm often smoked or grilled, with bones in, and slathered in BBQ sauce.
What can go up but never come down?
Very helpful if you intend to go gently down a river.
If itβs information you seek, come and see me. If itβs pairs of letters you need, I have consecutively three. What am I?