The formula with 3.2 substituted
miles = 3.2 ÷ 1.609344 = 1.988
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, 3.2 km takes about 38 minutes. At an easy running pace of 10 km/h it takes about 19. In metres it is 3,200.
What 3.2 kilometres means in practice
3.2 km is the two-mile run of the US Army fitness test, where the exact distance is 3.219 km, and eight laps of a 400 m track. That is why the value is searched for so often: it is the number soldiers, cadets and school athletes need.