Convert from block [East U.S.] to span

Unit Definition (block [East U.S.])
The Block is an informal unit of distance popular in the U.S. A block is the average distance between street intersections in the rectangular street grids common in most American cities. The length of a block in Eastern USA is about 1/20 mile or 80 meters.

Unit Definition (span)
Span is the width of a human hand, from the tip of the thumb to the tip of the pinky finger.