Photo: THINK A (Shutterstock)
Car mileage is usually discussed in “miles per gallon,” which generally makes sense: We calculate car usage in miles and pay for gas by the gallon. But when it comes to budgeting, we don’t always care how far we can go on a specific amount of a specific petroleum product. We care how much it costs. That goes double if we’re comparing cars that use different types of fuel, like a gas car versus an electric—or if we have a car that can use both.
Use MPD to compare traditional cars
Even if your car only runs on plain old gasoline, calculating your miles-per-dollar can help you put your budget into perspective. When gas was $5.09 this summer, a car that gets 22 miles per gallon would get you 4.3 miles per dollar. By comparison, a car that gets 30 miles per gallon gets you 5.9 miles per dollar.
You can find miles per dollar if you know your car’s mileage and your current local gas price:
(miles your car gets per gallon) / (price of gas, per gallon)
If you can’t remember which number goes first, just remember that it’s miles per dollar, so you take the number of miles (for example, 30) and divide it by the number of dollars ($5.09, ouch). That’s 5.9. If you prefer, you could flip the equation around to find dollars or cents per mile: in this same example, that would be 17 cents per mile.
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Use MPD to budget your driving
Miles per dollar can also be a helpful way of thinking about how much it costs you to drive somewhere. For example, I can work out at home, but I like to visit a gym that is nine miles away, so an 18-mile round trip. Using the example of a car that gets 5.9 miles per dollar, it costs me $3.05 every time I go to the gym, for $9.15 total if I go three times in a given week. Each day I stayed home this summer saved me three bucks. (Now that gas prices have dropped, each trip is slightly cheaper at $2.40.)
Or let’s say I want to go hike in a forest 50 miles away. That’s a 100-mile round trip. If my car gets 30 miles to the gallon, and my friend’s car gets 22, will we save a significant amount of gas money if we take my car instead of theirs? The difference amounts to $18 versus $13 if gas is $4/gallon. If we had taken the trip in the less-efficient car when gas prices were at their peak, we’d have been paying at least $23 for that trip.
Use MPD to compare cars that use different energy sources
Not all cars run on gasoline. Let’s say you’re looking at pickup trucks and you’re wondering if it’s better to buy a diesel or gas model. This year’s RAM 1500 comes in a gas version that gets 24 miles to the gallon on the highway, and a diesel that gets 29. Prices at a Sheetz near me are $4.03 per gallon for gas, $5.15 for diesel.
Crunch the numbers and the decision gets easier: we’ll get 6.0 miles per dollar with the gas engine, and only 5.6 for the diesel. If price is our only consideration, the gas car wins—but it’s not a huge difference, so we know we aren’t sacrificing too much if the diesel version is the better pick when we consider other factors. To put it in terms of yearly driving, if we cover 10,000 highway miles, we’ll pay $1,776 versus $1,681.
Use MPD to compare fuels for a plug-in hybrid
When my husband and I were shopping for a minivan and the possibility of getting a plug-in hybrid came up, one of the first things I did was work the numbers for how much it costs to run the car off electricity instead of gas. We’ll be saving gas, but will we really be saving money?
When a Chrysler Pacifica is running on gas alone, it gets about 30 miles per gallon. But the car also has a small battery with about a 33-mile capacity. That means a full charge of the battery is roughly equivalent to a gallon of gas.
At 15 cents per kilowatt hour (after taxes and fees), it costs about $2.40 to charge the battery, for 13.8 miles per dollar. That’s way cheaper than gas. We bought the car, and we make sure to keep it charged so we’re using as much electricity and as little gas as possible.
Recently, I took this same car on a road trip. One of the highway rest stops had an electric charger you could pay for. Hoping for a break from paying sky-high gas prices, I checked the rates. It cost 3 cents for every 30 seconds of charging.
I know that it takes about two hours to fully charge the battery with a level 2 charger (which this was), so I did a little math. A 33-mile charge would cost $7.20, giving us just 4.6 miles per dollar. Not only is that more expensive than our electricity at home, it’s way more than we’d pay for the equivalent (1.1 gallons) in gas. No, thank you! Meanwhile, one of our hotels had a free charging station. At a price of $0, that’s infinity miles per dollar. Much better.
