Always, for anything.
I mainly do smalls and take the picture of item next to a tape measure or framers square.
Rims I include lug patter size and link to site on how to measure yours for fit.
Furniture I give outside dimensions plus on drawer size...on chairs, the hieght of seat...tables, circumference....
Still get asked about size. Seems the more specific I get the more questions I get.
Usually asking questions clearly stated in Ad.
(I once got asked how tall a 6 foot corner lamp was!)
And, I still meet people and get "oh...I didn't realize it was so big/small"
But I figure the more info I give the better ground I stand on when they try to "negotiate" by saying its not what they thought it was.
I know others tht are purposely vague then "sell" the item once they get a meet. But I'm not a salesman, not my thing to talk people into buying.