Well, you by your electricity in United of kilowatt-hours (KWh). 1000w for 1hr is a KWh. In order to compare it to gas costs, you need is miles/kWh. (I’m assuming you’re in the US where you don’t calculate gas as Liters/100km).

The simplest thing you can do is take the range of the car, and divide by the size of the battery… (the EPA range you see here in the US is a good place to start)

So. We have a 1st Gen ioniq, which has a 38.5KWh battery, and it gets 170 miles per charge. So the math goes:

170 / 38.5 = 4.4 miles/kWh. (Which is really good)

(In reality, commuting at lower speeds we usually average 190miles/charge.)

Anyways, now that you have your miles/kWh, you go to your power bill and look at how much you’re paying per kWh. And how much gas costs.

So in our case we pay about $0.28/kWh and gas is $5.00/gallon.

So then you do ($gas) / ($kWh):

$5.00 / $0.28 = 17.8 you can buy 17.8kwh for the same as a gallon)

Next you multiply the kWh you can buy with the miles/kWh.

17.8 x 4.4 = 79 mpg based on epa mileage. And local electricity and gas costs.