The formula with 2.7 substituted
miles = 2.7 ÷ 1.609344 = 1.678
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, 2.7 km takes about 32 minutes. At an easy running pace of 10 km/h it takes about 16. In metres it is 2,700.
What 2.7 kilometres means in practice
2.7 km is 1.68 miles, a touch under seven laps of a running track. Many apps report 2.7 km for a 'twenty minute walk', which is a fair estimate at 5 km/h with a couple of road crossings.