Convert from span to block [South, West U.S.]

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

Unit Definition (block [South, West 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 is about 1/10 mile (160 meters) in USA cities in the South and West.