The eMPG is an attempt to convert WH/m into MPG based on some fixed numbers for $/kWh and $/gallon.

a WH/m x b $/kWh / 1000 = x $/mi

c $/ga gasoline / x $/mi = mpg equivalent.

For a=300, b=0.15, c=$3.00 you get 66mpg.

You can plug in your own numbers as you see fit.

The cost savings is then estimated by plugging in a number of miles driven, and comparing gallons of gas versus a hypothetically less efficient car (not sure what MPG rating Tesla uses for its comparison)

Note that the Tesla Model 3 is closer to 150 WH/mi. And what does gasoline cost in those European countries?