So I found the answer:  6.5 inches shorter, 3.3 inches narrower, and 4.6 inches lower.  If you happen to be pondering the same question I did, then these specifications might satisfy at least your initial curiosity as well.  Suffice to say– even with some challenge to the immediate naked eye– several key differences do exist between the new BMW X1 and its close sibling the X3.  We’ll soon see how well the X1 is received here in the U.S., eye-catching as this little guy is.  Of course success might depend on whether you choose to call it a crossover or an SU– pardon me– SAV.  As I’m not one for “crossovers” myself, let’s go with the latter.

The shorter, narrower, lower X1.

The longer, wider, taller X3.