1 french is exactly 1/3 millimeters. In SI units 1 french is 3.333... x 10-4 meters.
4 000 meters. A general or metric league of 4 kilometers. Leagues based on the mile are typically smaller at 3 miles, however there are many variations. Used by Jules Verne in 20 000 Leagues Under the Sea. 1 League (metric) = 4 000 meters (SI unit).