^this.
3.78L - US Gal
4.54L - Imperial
I add about 20% to the lies in my Mustang, it's not a science, it just makes me feel... better? Nope, cheated.
Managed 35.3mpg in the 4.4 TDV8 on a round trip from Maidstone to Falmouth over the weekend which I was very pleased with. I don't bother...