Fuel Consumption Calculator
Driving 650 km on 45 liters uses 6.92 L/100 km, 14.44 km/L, 33.98 US MPG, or 40.80 UK MPG. This fuel consumption calculator converts one trip's distance and fuel used into four common economy measures. Enter kilometers or miles and liters or US gallons. Gallon input always means a US gallon, while the UK MPG result is calculated separately with the larger imperial gallon.
Quick answer
Fuel consumption is fuel used divided by distance covered. The full-tank-to-full-tank method gives the most honest number.
Fuel consumption
6.92 L/100 km
km per liter
14.44
US MPG
33.98
UK MPG
40.8
What this tells you
- •Fuel consumption is fuel used divided by distance covered. The full-tank-to-full-tank method gives the most honest number.
- •L/100 km is the metric standard, and lower is better. MPG flips the ratio, so higher is better.
- •US and UK MPG differ because the UK gallon is 20 percent bigger.
- •The calculation describes the entered trip and does not guarantee the same result on another route, season, load, or driving style.
- •Mile input converts at exactly 1.609344 kilometers per mile for this calculation.
- •US gallon input converts at 3.785411784 liters, while UK MPG uses 4.54609 liters per imperial gallon.
- •All four displayed measures are rounded to 2 decimal places.
How to Use
- 1For a pump-to-pump check, fill consistently and note the odometer or reset the trip meter.
- 2Drive a useful distance, then refill under similar conditions and record the amount dispensed.
- 3Enter the distance and select kilometers or miles.
- 4Enter fuel used and select liters or US gallons. Do not enter an imperial-gallon amount as gallons.
- 5Calculate and compare L/100 km, km/L, US MPG, and UK MPG.
- 6For budgeting, multiply a separately verified fuel quantity by a current local price. This tool itself does not calculate cost.
How It Works
Formula
L/100 km = (liters used / km driven) x 100Convert the trip to kilometers and liters first. L/100 km is liters divided by kilometers times 100, while km/L reverses that ratio. MPG converts kilometers to miles and liters to the selected gallon standard. For 650 km and 45 L, consumption is 45 / 650 x 100 = 6.9231 L/100 km, displayed as 6.92. Economy is 650 / 45 = 14.4444 km/L. The trip is 403.8913 miles and 45 liters is 11.8888 US gallons, producing 33.98 US MPG. Using imperial gallons produces 40.80 UK MPG.
Calculation note: values are processed in the order shown above, using the current input units.
Worked Examples
Mid-size car on a mixed route
Forty-five liters divided by 650 km and multiplied by 100 gives 6.92 L/100 km. The reciprocal measure is 14.44 km/L.
US road trip in miles and gallons
Four hundred miles converts to 643.7376 km and 12 US gallons converts to 45.4249 liters. Those values produce all four displayed results.
Efficient hybrid in the city
Twenty-two liters over 500 km gives 4.40 L/100 km. Dividing 500 by 22 gives 22.73 km/L, which converts to 53.46 US MPG.
Higher-consumption trip
Thirty liters over 300 km is exactly 10 liters per 100 km and 10 km per liter. Converting the same trip gives 23.52 US MPG and 28.25 UK MPG.
250 miles on 8 US gallons
The direct US measure is 250 / 8 = 31.25 MPG. After converting distance and volume, the equivalent metric consumption is 7.53 L/100 km.
L/100 km to MPG Conversion
How the metric and US measures line up.
| L/100 km | km/L | US MPG |
|---|---|---|
| 4.0 | 25.0 | 58.8 |
| 5.0 | 20.0 | 47.0 |
| 6.0 | 16.7 | 39.2 |
| 7.0 | 14.3 | 33.6 |
| 8.0 | 12.5 | 29.4 |
| 10.0 | 10.0 | 23.5 |
| 12.0 | 8.3 | 19.6 |
Values are approximate and use US MPG. UK MPG is higher for the same trip because an imperial gallon is larger.
Why L/100 km and MPG move in opposite directions
L/100 km measures fuel consumed for a fixed distance, so a lower number means better economy. MPG and km/L measure distance traveled for a fixed fuel amount, so a higher number means better economy.
The relationship is reciprocal rather than linear. Improving from 12 to 10 L/100 km saves more fuel over the same distance than improving from 6 to 4 L/100 km by a simple percentage comparison might suggest. Compare actual fuel used for the distance you expect to drive.
US and UK MPG must always be labeled. The vehicle and trip do not change, but the numerical UK result is larger because an imperial gallon contains more liters.
Common mistakes
- Trusting the dashboard readout alone. Onboard computers often flatter by 5 to 10 percent. The pump-to-pump method is the ground truth.
- Mixing gallon standards. 40 MPG on UK gallons is only 33 MPG on US gallons, the same car and the same fuel.
- Measuring a single short trip. Cold starts burn extra fuel, so measure across at least a few hundred kilometers for a stable figure.
- Entering the tank's rated capacity instead of the fuel actually used during the measured distance.
- Treating a dashboard estimate as identical to a pump measurement without checking how the vehicle calculates it.
- Comparing two MPG values without confirming whether each uses US or imperial gallons.
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