Grand pianos and their designations.

[Vinny Samarco]

Hi Everyone,
    When dealing with customers about grand pianos, I have two questions:
When someone  says to me, I have a grand  piano that is 6 foot, 1 inches, 
etc. where do they measure to get those figures?
The second question is: is the term "baby grand" just a commercial 
product-selling term (like upright grand which has no meaning)
with a specific length, or should we talk to our customers about small 
grands, and large grands?

Thanks for your help.
Vinny Samarco