Trip Fuel Cost

This calculator estimates fuel cost for a trip from three inputs -- Trip Miles, MPG (fuel economy), and $/Gallon (local gas price) -- using Gallons = Trip Miles divided by MPG, then Est. Fuel Cost = Gallons times $/Gallon. Because Est. Fuel Cost is a product of Trip Miles, $/Gallon, and the inverse of MPG, all three inputs move it by an essentially equal share in percentage terms: raising Trip Miles or $/Gallon raises the cost by roughly the same proportion, and raising MPG lowers it by close to that same proportion, so no single input dominates the total -- they all matter about equally.

$/100 Mi, by contrast, works out to exactly $/Gallon divided by MPG times 100: because the Trip Miles term cancels out of that ratio algebraically, this per-100-mile cost figure is completely unaffected by how long your actual trip is -- a one-mile errand and a cross-country drive at the same MPG and gas price show the identical $/100 Mi. Gallons Needed similarly ignores $/Gallon entirely, since it's purely Trip Miles divided by MPG. This is a simple linear model: it does not account for highway vs. city driving splits, elevation change, idling in traffic, or a vehicle's real-world MPG varying with speed and load.