Judging by the whippets I've seen about 100km2 should be about right 
I don't really have a good answer but I would logic it out like this: A whippet can run about 35mph. That's about 50ft a second. In an enclosure of 30x20ft your dog won't really be able to run, if that's your goal. You'll have to organize it so they can run off leash during your walking time. Maybe you have some kind of a facility or a beach nearby that would accommodate that.
I don't really have a good answer but I would logic it out like this: A whippet can run about 35mph. That's about 50ft a second. In an enclosure of 30x20ft your dog won't really be able to run, if that's your goal. You'll have to organize it so they can run off leash during your walking time. Maybe you have some kind of a facility or a beach nearby that would accommodate that.
