If it's been a while since you and your friends have seen the first Harry Potter movie, Harry Potter and the Sorcerer's Stone (2001), you may be ready to for a movie marathon! Altogether, the Potter films will take about 20 hours to watch start to finish, so you and your crew have your viewing cut out for you.
Fall damage is 1 (half heart) for each block fallen after the third. Thus falling 4 blocks causes 1 half heart damage, 2 (full heart) damage for 5 blocks, 3 (heart and a half) for 6 blocks and so forth.
This equals approximately 16 or 17 blocks per mile. Cities are not always consistent in the size of blocks. But, it seems that most of the "standard" rectangular blocks are: 10 to 11 blocks per mile if walking the long side, and 16 to 17 blocks per mile if walking the short side.