Calculate MPGe from miles driven and kWh used, convert MPGe to mi/kWh and kWh per 100 miles, and find your EV cost per mile and the gas MPG it matches.
MPGe Formula
MPGe = 33.7 * mi / kWh
Cost per mile = (33.7 * Pe) / MPGe
Gas MPG cost match = (MPGe * Pg) / (33.7 * Pe)
- MPGe is the miles per gallon of gasoline equivalent
- mi is the distance driven in miles
- kWh is the electricity drawn at the wall over the matching distance, in kilowatt hours; battery energy is divided by your supplied charging efficiency first
- 33.7 is the EPA energy equivalence of one gallon of gasoline, in kWh (33.705 kWh before rounding)
- Pe is the electricity price in dollars per kWh
- Pg is the gasoline price in dollars per gallon
The first formula drives the trip mode of the calculator. Enter the distance you drove and the kWh you used, and it returns your MPGe along with the same efficiency expressed as miles per kWh, kWh per 100 miles, Wh per mile, kilometers per kWh, and kWh per 100 km. If your kWh number comes from the car trip meter instead of the wall charger, the calculator divides it by your charging efficiency first, since the trip meter only sees energy leaving the battery. EPA ratings count energy drawn at the wall. This adjustment estimates the same energy boundary, but a real trip does not reproduce EPA laboratory procedures. The wall-basis MPGe estimate equals the battery-basis equivalent multiplied by charging efficiency divided by 100.
The convert mode applies the same 33.7 kWh equivalence in reverse. Any one of the six efficiency units fixes all the others, so entering a value in one unit returns the full set.
The cost mode uses the second and third formulas. Cost per mile is your electricity price multiplied by the energy your EV needs per mile. The gas MPG cost match tells you what fuel economy a gasoline car would need to run at the same cost per mile given current gas prices. It is the most direct way to translate an MPGe rating into money.
MPGe Conversion Chart and Cost Equivalents
The table below converts common MPGe ratings into the other efficiency units used on EV window stickers and in car trip computers. The rows are illustrative efficiency values, not a current vehicle ranking.
| MPGe | Miles per kWh | kWh per 100 miles | Wh per mile |
|---|---|---|---|
| 60 | 1.78 | 56.2 | 562 |
| 70 | 2.08 | 48.1 | 481 |
| 80 | 2.37 | 42.1 | 421 |
| 90 | 2.67 | 37.4 | 374 |
| 100 | 2.97 | 33.7 | 337 |
| 110 | 3.26 | 30.6 | 306 |
| 120 | 3.56 | 28.1 | 281 |
| 130 | 3.86 | 25.9 | 259 |
| 140 | 4.15 | 24.1 | 241 |
| 146 | 4.33 | 23.1 | 231 |
MPGe compares energy, not money, so a 120 MPGe EV does not cost the same to run as a 120 MPG gas car would. This table shows what fuel economy a gasoline car would need to match each MPGe rating on cost per mile, using example prices of $0.18 per kWh for electricity and $3.80 per US gallon for gasoline. These are illustrative inputs, not current national averages.
| MPGe | Cost per mile at $0.18/kWh | Cost per 100 miles | Gas MPG cost match at $3.80/gal |
|---|---|---|---|
| 60 | 10.1¢ | $10.11 | 37.6 MPG |
| 80 | 7.6¢ | $7.58 | 50.1 MPG |
| 100 | 6.1¢ | $6.07 | 62.6 MPG |
| 120 | 5.1¢ | $5.06 | 75.2 MPG |
| 140 | 4.3¢ | $4.33 | 87.7 MPG |
Prices change the picture quickly. The same 100 MPGe EV charged on a DC fast charger at $0.45 per kWh costs about 15.2 cents per mile, which matches a gas car getting only about 25 MPG. Charging at home off peak for $0.10 per kWh drops it to 3.4 cents per mile, a match for a 113 MPG gas car. Run your own rates through the cost mode of the calculator to see where your charging mix lands.
Example Problems
Example 1. You drive 180 miles and your AC input meter reports 45 kWh drawn from the wall to recharge the battery. Your efficiency is 180 / 45 = 4.0 miles per kWh. Applying the formula, MPGe = 33.7 * 180 / 45 = 134.8 MPGe. That is equivalent to 25 kWh per 100 miles.
Example 2. Your EV is rated at 115 MPGe, you pay $0.18 per kWh, and gas in your area costs $3.80 per gallon. Energy use is 3370 / 115 = 29.3 kWh per 100 miles. Cost per mile = (33.7 * 0.18) / 115 = $0.053, or $5.27 per 100 miles. The gas MPG cost match = (115 * 3.80) / (33.7 * 0.18) = 72 MPG, so a gasoline car would need to average 72 MPG to run this cheaply. Over 12,000 miles per year, charging costs about $633.
Frequently Asked Questions
Why is my calculated MPGe lower than the EPA rating on my window sticker?
Two different measurements are usually being compared. Your car trip meter counts energy leaving the battery, while the EPA rating counts energy drawn from the wall, which includes charging losses. Losses vary with equipment and conditions. Cold weather, high speeds, and climate control use also cut real world efficiency well below the laboratory based rating. If you compute MPGe from trip meter kWh, select Battery / car meter and supply a charging-efficiency estimate. The result uses an estimated wall-energy boundary; it is not an official EPA rating.
Is the 33.7 kWh per gallon figure exact?
The EPA equivalence is 33.705 kWh per gallon, derived from the roughly 115,000 BTU of energy in a gallon of regular gasoline. EPA consumer guidance expresses this as 33.7 kWh, which is what this calculator uses, and the difference changes results by less than 0.02 percent. Note that the figure is an energy equivalence only. It says nothing about what the two fuels cost.
Does a higher MPGe always mean lower running costs than a gas car?
No. MPGe compares energy content, and electricity and gasoline are priced very differently per unit of energy. At the example prices of $0.18/kWh and $3.80/US gal, a 120 MPGe EV has about the same energy cost per mile as a 75 MPG gas car. The same EV relying on expensive DC fast charging can cost as much per mile as an ordinary 30 MPG sedan. Higher MPGe means less energy per mile on the same measurement basis, but lower cost also depends on the electricity and gasoline prices, so check your own numbers with the cost mode.
