No size under Specs?
You pick the size you want from the dropdown. 
ding ding ding
Physical size?
Capacity and size are two different things
I ordered one of the 750gb models and was a little shocked to see that it was sent “loose” with out a box. It had about two layers of large bubble wrap around it and then placed into a plastic shipping bag. It would seam though that FedEx was extremely gentile with it as so far it seams to have no issues. Instantly recognized has 698gb worth of writable space on it which is expected. I purchased for use with my Roku 3 and am very happy, so far. Now we play the waiting game to see longevity. My old portable WD HD I purchased new back in 08 made it through a year long deployment and still is kicking to this day. So one would think if this one just sits on the entertainment center it should last just as if not longer than the other one… tic toc, tic toc, your move WD.