Compare both vehicles over the same distance
For an EV rated in miles per kilowatt-hour, divide miles by that efficiency to estimate energy delivered to the battery. For a combustion vehicle rated in miles per gallon, divide the same miles by MPG to estimate gallons. Other unit systems work too, but distance and efficiency units must match.
Cost per mile is useful for recurring comparisons: divide total energy cost by distance. It does not capture purchase price, finance, maintenance, insurance, taxes, depreciation, or travel time, so label it as energy cost rather than total ownership cost.
Calculate fuel cost on a matching basis
For a vehicle expressed in miles per gallon, gasoline cost equals distance divided by MPG, multiplied by price per gallon. If consumption is expressed as litres per 100 kilometres, multiply kilometres by L/100 km and divide by 100 before applying price per litre.
Use the marginal price likely to apply to the trip. Electricity tariffs may vary by time, usage tier, location, session, or subscription; fuel prices vary by station and date. Averaging a bill can be useful, but fixed household charges may not rise with one additional charging session.
Worked example: a 180-mile trip
Compare an EV achieving 3.6 miles per battery kWh with a gasoline vehicle achieving 30 MPG over 180 miles. Assume 90% charging efficiency, electricity at $0.18 per kWh drawn, and gasoline at $3.50 per gallon. These are illustrative inputs, not price forecasts.
Build a realistic range rather than one forecast
Temperature, speed, elevation, traffic, payload, tires, cabin heating or cooling, and short-trip behavior can move efficiency away from a rating. For charging, preconditioning, battery temperature, charger power, tapering, and accessory use can affect energy drawn and time connected.
Run low, middle, and high price or efficiency cases. Separate home and public charging, and include session or parking fees when they apply. Actual trip data and receipts provide better personal inputs than a generic vehicle rating.
Assumptions and limitations
Assumptions used in the explanations
- Both vehicles travel the same 180-mile route under the modeled comparison.
- The stated efficiencies and prices remain constant for the entire trip.
- EV charging efficiency is 90%, so charger energy exceeds battery energy.
What this guide cannot tell you
- The comparison covers propulsion energy only, not total vehicle ownership or travel costs.
- Efficiency and charging losses vary with conditions, vehicle, charger, driving style, and measurement method.
- Tariffs, taxes, fees, subscriptions, and fuel prices differ by location and can change over time.
This guide provides general educational information, not financial, tax, legal, or lending advice.
Frequently asked questions
Why is energy drawn from a charger higher than energy added to the battery?
Some energy is used by conversion, thermal management, electronics, and other charging processes. The difference varies, so a charging-efficiency assumption should be visible.
Should I use my full electricity bill rate?
Use the price that best represents additional charging, including time or tier effects and applicable variable charges. Treat fixed charges separately if they would exist without the session.
Can I compare mi/kWh directly with MPG?
No. They use different energy units. Convert each vehicle’s efficiency into energy cost for the same distance, then compare cost per trip or per mile.
Does lower trip energy cost mean lower total ownership cost?
Not necessarily. Purchase, finance, depreciation, insurance, maintenance, taxes, and charging equipment are outside a trip-energy comparison.