The formula with 1.6 substituted
miles = 1.6 ÷ 1.609344 = 0.994
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, 1.6 km takes about 19 minutes. At an easy running pace of 10 km/h it takes about 10. In metres it is 1,600.
What 1.6 kilometres means in practice
1.6 km is the everyday shorthand for one mile, and it is very slightly under: a mile is 1.609344 km, so 1.6 km falls 9.3 metres short. Fitness apps that show 1.61 km for a one mile run are rounding the other way.