Convert from gnat's eye to ri [Japan]

Unit Definition (gnat's eye)
The gnat's eye is an idiomatic "unit" of distance; it's common to hear that something is "as small as a gnat's eye". In fact, the eyes of typical gnats tend to have diameters similar in size to a hair's breadth: roughly 100-150 micrometers (0.10-0.15 millimeters).

Unit Definition (ri [Japan])
The ri is a traditional Japanese unit of distance, sometimes called the Japanese league because it is of similar length to the European league. The ri equals 2160 ken or 12 960 shaku (the shaku being the Japanese equivalent of the foot). This is about 3927 meters or 2.44 statute miles.