The formula with 1.4 substituted
miles = 1.4 ÷ 1.609344 = 0.870
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, 1.4 km takes about 17 minutes. At an easy running pace of 10 km/h it takes about 8. In metres it is 1,400.
What 1.4 kilometres means in practice
At 1.4 km you are close to seven eighths of a mile. It is a typical length for a park loop or an airport walk from security to a far gate, and it takes around 16 minutes at an ordinary pace.