Awww, Streak is adorable!!!
Sinduction, the Italian greyhounds are the little ones. They typically range from maybe 9 or 10 pounds to the teens. My littlest one is only 12" tall and weighs 6.7 pounds. My largest is about 16" tall.
Whippets are a medium size dog. Larger than my little Italians, but smaller than the racing greyhounds. A typical whippet, if I remember correctly, might weigh in the 30s, and a greyhound typically in the 60s or more (pounds). To someone unused to them, the three breeds look pretty much like three sizes of one breed. But the greyhounds and Italian greyhounds are very old breeds. The whippets were created by cross-breeding to create a "common man's" racing dog, and are much more recent/new a breed. They're all wonderful.