Gas Mileage Calculator
Measure real-world fuel economy from a trip, odometer readings, or several fill-ups. See US and Imperial MPG, km/L, L/100 km, cost and planning estimates.
Full Gas Mileage GuideTransparent methodology
How gas mileage is calculated
1. Measure distance
Use a trip reading or subtract the starting odometer from the ending reading.
2. Record fuel
Use the amount needed to refill to the same full-tank level, with the correct gallon or litre unit.
3. Calculate economy
Distance divided by fuel gives MPG or km/L. L/100 km expresses consumption, so lower is better.
4. Weight several tanks
Total distance divided by total fuel produces the correct multi-fill-up average.
Worked example
Driving 300 miles and adding 10 US gallons gives 30 MPG (US), about 36.03 MPG (Imperial), 12.75 km/L, or 7.84 L/100 km.
Answers before you measure
Frequently asked questions
How do I calculate gas mileage?
Fill the tank, reset the trip meter, drive normally, then refill to the same level. Divide miles driven by US gallons added to get US MPG.
Should I use trip distance or odometer readings?
Either works. Trip distance is faster; subtracting starting mileage from ending mileage is useful when you did not reset the trip meter.
How should I average several fill-ups?
Add every distance and every fuel amount, then divide total distance by total fuel. Do not average the individual MPG readings because fill-ups can cover different distances.
What is the difference between US and Imperial MPG?
An Imperial gallon is larger than a US liquid gallon, so the numeric MPG values differ. This calculator displays both without treating them as interchangeable.
Is higher MPG always better?
For MPG and km/L, higher means better fuel economy. For L/100 km, lower is better because it describes fuel consumed per 100 kilometres.
Why is my calculated MPG different from the dashboard?
Dashboard figures may estimate fuel flow and can use different averaging periods. Pump shutoff, fill level, idling, traffic and conditions also affect a tank calculation.
How many fill-ups give a reliable average?
Two intervals are enough to calculate an average, but several full-tank intervals over typical driving usually give a more representative result.
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