Calculate your vehicle's gas mileage (MPG) from two odometer readings and the gas added, plus fuel cost.
Record your odometer reading when you fill up, then fill up again next time and record both the new reading and how many gallons it took to fill the tank. The difference in odometer readings divided by the gallons added gives your gas mileage — this works because that fill-up's gallons are what it took to drive the miles since the previous fill-up.
Driving style, terrain, tire pressure, vehicle load, and even weather all affect fuel efficiency. A single fill-up's MPG is a snapshot — averaging several fill-ups gives a more representative figure for your typical driving.
This method assumes you filled the tank completely both times — a partial fill-up will throw off the gallons-per-mile calculation.
It varies enormously by vehicle type — compact cars often reach 30+ MPG while trucks and SUVs may be in the teens. Compare against your specific vehicle's EPA rating for context.
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