how to work out my mpg?

[almoststew1990]

How can I work out my mpg in an old car which doesn't have a mpg-o-meter?

Yes I know I can see how far I go on one tank and use my tank size to work out fuel per mile etc etc but I don't completely completely drain my tank, I overfill my tank and my tank probably has 19 years of crap resting in the bottom of it. Also my fuel gauge readings are rather unhelpfully not equally spaced- 3/4 full is more like 13/16 and a quarter full is more like 1/5

Anyone got any tips?

 

[almoststew1990]

I know when it was new it was 50l.

 

[almoststew1990]

I forgot i get the actual fuel amount from the pump that was the missing info I need Boom thanks!