The formula with 26 substituted
L/100km = 235.214583 ÷ 26 = 9.05
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 MPG to L/100km Converter explains where each comes from and gives a longer table.
The same 26 mpg (US) is 31.22 mpg on the imperial gallon, 9.05 L/100km and 11.05 km/L. If your 26 mpg figure came from a British source it already uses the imperial gallon, and the metric answer is 10.86 L/100km instead.
What 26 mpg (US) means in practice
26 mpg (US) converts to 9.05 L/100km. It is typical for a compact SUV with all-wheel drive, and a little below the EPA's reported average for new vehicles in recent years.