Kentucky Derby - 1.25 mile
Preakness Stakes - 1.1875 mile
Belmont Stakes - 1.50 mile
Of course, part of why it's such a famous trio of races is the varying lengths - to win all three a horse has to be strong and versatile - you can take the first two with a sprinter, but the Belmont requires speed and stamina.
It should be a good race to watch - it will be fun to see what happens. Apparently the Preakness distance phased his Smarty-ness not at all: not only did he come in some 11-plus lengths ahead of the rest of the field, he apparently was looking for more, on the order of "we have to STOP now? I was just getting into it!"
[See, my horse craziness didn't so much go away as mutate. And hey - pastern was the answer to a crossword clue yesterday, so its even been of use.]