Fuel is the visible cost and rarely the largest
Ask what a mile costs and most people answer with fuel, because fuel is the part you pay for at a counter and watch on a display. It is usually a minority of the true figure.
Depreciation attributable to mileage, tires, brakes, servicing intervals driven by distance, and a share of insurance all scale with how much you drive, and none of them announces itself. A per-mile figure that includes them is typically several times the fuel-only number, which is why decisions made on fuel alone -- whether to drive rather than take transit, whether a cheaper house further out is cheaper overall -- come out wrong so often.
The tools here let you enter a per-mile wear figure explicitly rather than pretending it is zero. Building your own is straightforward: total what you spent on tires, servicing and repairs over a year, add the mileage-driven share of depreciation, and divide by the miles you drove.
The mpg illusion
Miles per gallon is an efficiency: distance per unit of fuel. Liters per 100 kilometers is a consumption: fuel per unit of distance. They describe the same thing and behave completely differently, because one is the reciprocal of the other.
The consequence is not intuitive. Improving from 15 to 20 mpg saves far more fuel over the same distance than improving from 40 to 50 mpg, even though the second change is larger in both absolute and percentage terms. Over 12,000 miles, the first saves 200 gallons and the second saves 60.
If you are comparing vehicles, or deciding which of two cars in a household to replace, convert to gallons per 10,000 miles -- or use the metric consumption figure -- and the comparison stops being misleading.
Measure, do not assume
Rated fuel economy comes from standardized test cycles and is a reference point, not a prediction of your driving. Cold starts, short trips, sustained speeds above roughly 55 mph, roof racks, under-inflated tires, idling and air conditioning all move real economy down, sometimes substantially.
Measuring your own takes two fill-ups and a trip meter: fill to the same point both times, drive at least 200 miles, and divide. A trip computer is convenient but usually reads optimistic. Tracking the figure over time is also the cheapest mechanical diagnostic available -- a sudden drop is a symptom.
Comparing an EV honestly
Energy cost per mile is the easy part of that comparison and the part these tools cover. Charging losses mean the energy drawn from the wall exceeds what reaches the battery, and the gap between charging at home and charging on a public fast network is large enough to change the conclusion entirely for someone without a driveway.
Purchase price, financing, insurance, depreciation, incentives and charger installation sit outside the model and frequently matter more than the running cost. Treat the result as one input among several.