dpeends on the car. My Zoe does 4.8 miles per kwhr, my old car does 35 miles per gallon (or 7.6 miles per litre) petrol is currently £1.6 a litre.
Which is 21p per mile, for my petrol car
at 98p a kwhr its 20p per mile.
but in practice the electric car is 3 pence a mile for me (average car charging price for me is 15p a kwhr)