The formula with 100 substituted
miles = 100 ÷ 1.609344 = 62.137
The constant is an exact definition, not a rounded factor: the mile is 1.609344 km, the US gallon is 3.785411784 litres and the imperial gallon is 4.54609 litres. The Kilometres to Miles Converter explains where each comes from and gives a longer table.
At a walking pace of 5 km/h, 100 km takes about 1200 minutes. At an easy running pace of 10 km/h it takes about 600. In metres it is 100,000.
What 100 kilometres means in practice
100 km is 62.14 miles, the classic ultramarathon distance and a common cycling sportive length. As a driving distance it is about an hour on a motorway, and it is the reference distance behind the L/100km fuel economy unit.