How do you determine an Electric car's MPG?

All electric vehicles have a listing of equivalent MPGe from the manufacturers, it's not just Cargurus.

The government has a formula for gas mileage equivalent. Tesla's come with different battery capacity. Ask the seller what range they get.

Thank you both for your answers. :) I found an article that explained it quite well. Basically, 33 kwh yields 100 miles of range (as standard unit of equivalence) and would thus be the equivalent of a "gallon of gasoline". So using that basis, a 60 kwh battery would yield a total range of almost 200 miles (when full), making the MPGe 90-93 miles per "gallon". So, I guess if a Tesla Model S 60 were an ICE car, it would have a 2 gallon gas tank, which by ICE standards would have really exceptional mileage. :) Thanks again! :) Knowing is half the battle.