When Forget miles per gallon—here’s the best metric for measuring a car’s efficiency

This is the gallons-per-100-miles rating. Although it is in smaller type than the miles-per-gallon number, it should figure larger in your calculations when comparing cars. That’s because the gallons/100 miles rating makes it easier to compare the efficiency of different cars and estimate their likely annual fuel cost. European countries measure fuel economy by the benchmark of “liters per 100 kilometers.” A lower number is better, and the moon-shot goal there is the “three-liter” car that scores 3.0 liters/100 km. That’s one that burns no more than 3 liters (about 3 quarts) of fuel to drive 100 km (62 miles). The advantage of measuring fuel consumption this way is that it makes comparisons easier fuel efficiency improves for a specific vehicle. That’s because the differences are linear. With miles per gallon, efficiency is graded on a curve. For example, for a 15-mpg car, a 5-mpg improvement is a 33-percent gain. But that same 5-mpg upgrade for a 30-mpg car is only a 17.5-percent improvement to a vehicle that is already using half as much gas. A good goal may then be 1 gallon per 100 miles—the ultimate accomplishment for combustion vehicles before they drive into the sunset as EVs gain popularity. That score also works out to 100 which might make it easier for people to understand this more useful benchmark. And just as we’ve started learning about a better way to measure gas-guzzling vehicles, we will inevitably have to learn more about batteries as we start buying EVs. The EPA rates them in kilowatt-hours per 100 miles, in the same general way that the new gallons-per-100-miles metric works for vehicles with combustion engine work. This is the gallons-per-100-miles rating. Although it is in smaller type than the miles-per-gallon number, it should figure larger in your calculations when comparing cars. That’s because the gallons/100 miles rating makes it easier to compare the efficiency of different cars and estimate their likely annual fuel cost. European countries measure fuel economy by the benchmark of “liters per 100 kilometers.” A lower number is better, and the moon-shot goal there is the “three-liter” car that scores 3.0 liters/100 km. That’s one that burns no more than 3 liters (about 3 quarts) of fuel to drive 100 km (62 miles). The advantage of measuring fuel consumption this way is that it makes comparisons easier fuel efficiency improves for a specific vehicle. That’s because the differences are linear. With miles per gallon, efficiency is graded on a curve. For example, for a 15-mpg car, a 5-mpg improvement is a 33-percent gain. But that same 5-mpg upgrade for a 30-mpg car is only a 17.5-percent improvement to a vehicle that is already using half as much gas. A good goal may then be 1 gallon per 100 miles—the ultimate accomplishment for combustion vehicles before they drive into the sunset as EVs gain popularity. That score also works out to 100 which might make it easier for people to understand this more useful benchmark. And just as we’ve started learning about a better way to measure gas-guzzling vehicles, we will inevitably have to learn more about batteries as we start buying EVs. The EPA rates them in kilowatt-hours per 100 miles, in the same general way that the new gallons-per-100-miles metric works for vehicles with combustion engine work.