Calculate your gas mileage the classic, accurate way — from odometer readings between two fill-ups. Get MPG, your fill-up cost and your cost per mile.
✓ Formula shown openly • ✓ Reviewed October 2026 • ✓ Free — no sign-up • ✓ Nothing you enter is stored
Gas Mileage Calculator
Formula: MPG = (Current − Previous Odometer) ÷ Gas Added • Nothing is stored.
Fill your tank and note the odometer (or reset the trip counter). Drive normally. At the next fill-up, note the new odometer reading and exactly how many gallons the fill took. The miles between the two readings, divided by the gallons added, is your true gas mileage.
Previous reading 45,000, current reading 45,360 — that is 360 miles. The fill took 12 gallons: 360 ÷ 12 = 30.00 MPG. At $3.50 a gallon the fill cost $42.00, and your fuel cost per mile is about $0.12.
The method assumes you filled up at both readings. If either fill was partial, the gallon figure will not match the miles and the MPG will be off — wait for two full fills.
How far one dollar of fuel takes you: MPG ÷ price per gallon. At 30 MPG and $3.50, that is 8.57 miles per dollar — a handy way to compare prices at different stations.
Tire pressure first (1 PSI low on all tires can cost ~0.2% each, and under-inflation is common), then air filter, spark plugs and any new roof cargo or heavier loads.
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