20,000 X 3 = 60,000.............
You know, I noticed that, too.
Sorry.
One source:
a nautical mile is equal to 1.151 statute miles. Or put another way a nautical mile equals 6076.12 feet. So 20,000 leagues = 60,000 nautical miles = 69,060 statute miles.
Another.
20,000 metric leagues (80,000 km, over 40,000 nautical miles), nearly twice the circumference of the Earth.
A league is 4,828.03 meters, approximately 3 miles.
20,000 leagues equal about 60,000 miles as you said.