How is MPG calculated from a fill-up?

Miles per gallon is simply distance travelled divided by gallons of fuel added to refill the tank. For the cleanest reading, fill the tank fully both before and after the trip so the fuel added equals the fuel actually burned.

How do you convert between MPG and L/100km?

They are reciprocal measures on different units. The tool converts your distance to kilometres and fuel to litres, then computes litres times 100 divided by kilometres. Higher MPG corresponds to lower L/100km, since L/100km measures consumption rather than efficiency.

Where does the CO2 figure come from?

Burning one US gallon of gasoline releases about 19.6 pounds, or 8.887 kilograms, of carbon dioxide, the EPA standard figure. The tool multiplies your gallons burned by 8.887 kg. Diesel produces roughly 15 percent more CO2 per gallon because it is denser.

Why measure economy per trip instead of trusting the dashboard?

Dashboard readouts estimate consumption from sensors and can drift by several percent. A measured fill-up to fill-up calculation is the ground truth, which is why it is the method used for fuel-economy comparisons and warranty disputes.

Can I track several fill-ups?

Each calculation covers one trip and fill-up. To find a rolling average, sum the total distance and total fuel across several tanks and enter those totals, which averages out the variation from how full each tank was.

Fuel Economy by Trip Calculator

The only way to know your true fuel economy is to measure it from a real fill-up. This calculator takes the distance you drove and the fuel you added, then reports MPG, L/100km, the cost of that fuel, and the carbon dioxide it produced.

How it works

Economy is computed directly from distance and volume, with unit conversions applied so both measures are shown:

US MPG    = miles / US gallons
L/100km   = litres × 100 / km
1 US gallon = 3.785411784 L      1 mile = 1.609344 km
CO₂       = gallons × 8.887 kg   (19.6 lb per gallon, gasoline)
cost      = fuel added × price per unit

Distance can come from your odometer start and end readings or from a direct trip figure, whichever you have.

Example and tips

Drive 320 miles and refill with 10 gallons and you get 32.0 MPG, about 7.35 L/100km, and roughly 88.9 kg of CO₂ for that fuel. For accuracy, always fill the tank to the same point at both ends of the measured trip — a fill-up to fill-up reading is the ground truth that dashboard estimates only approximate. To smooth out tank-to-tank variation, add up several tanks of distance and fuel and enter the totals for a rolling average.