Fuel Economy Calculator
Calculate your vehicle’s fuel economy from distance traveled and fuel used. See the result instantly in L/100 km, km/L, US MPG and UK MPG.
Calculate Fuel Economy
Enter how far the vehicle traveled and how much fuel it used. ToolZippy converts the result into four common fuel-economy units.
How to Use the Fuel Economy Calculator
The ToolZippy Fuel Economy Calculator calculates vehicle efficiency from two measurements: the distance traveled and the amount of fuel consumed over that distance.
Enter your distance in kilometers or miles, then enter fuel used in liters, US gallons or UK/Imperial gallons. The calculator converts those measurements internally and displays four common fuel-economy formats at the same time.
This makes it easier to compare a vehicle specification expressed in MPG with a trip record measured in liters and kilometers without manually converting every value.
Example: 500 km Using 40 Liters
Suppose your vehicle traveled 500 kilometers and consumed 40 liters of fuel.
The same fuel economy can also be expressed as approximately:
L/100 km Formula
Liters per 100 kilometers measures how much fuel is consumed to travel 100 km.
For example, a vehicle using 6 L/100 km consumes less fuel over the same journey than a vehicle using 9 L/100 km.
km/L Formula
Kilometers per liter measures how far the vehicle travels using one liter of fuel.
This is the inverse style of L/100 km. Therefore, the direction of “better” economy is different: lower is better for L/100 km, while higher is better for km/L.
US MPG Formula
US MPG means miles per US gallon. It tells you how many miles the vehicle can travel for each US gallon of fuel.
A higher US MPG figure represents better fuel economy because the vehicle travels farther on the same gallon of fuel.
UK / Imperial MPG Formula
UK MPG uses the Imperial gallon rather than the US gallon.
Because an Imperial gallon is larger than a US gallon, the numerical UK MPG figure is higher than the US MPG figure for the same vehicle efficiency.
Understanding the Four Results
| Unit | Meaning | Better Economy | Example |
|---|---|---|---|
| L/100 km | Liters required for 100 km | Lower number | 8 L/100 km |
| km/L | Kilometers traveled per liter | Higher number | 12.5 km/L |
| US MPG | Miles traveled per US gallon | Higher number | 29.4 MPG |
| UK MPG | Miles traveled per Imperial gallon | Higher number | 35.3 MPG |
How to Measure Real Fuel Economy
A practical way to estimate real-world fuel economy is to compare fuel consumed with distance traveled over the same period.
For a tank-to-tank measurement:
- Fill the fuel tank and record the odometer or reset the trip meter.
- Drive normally until the next refueling.
- Record the distance traveled.
- Refill the tank and record how much fuel was added.
- Enter that distance and fuel amount into the calculator.
Using a longer driving period can provide a more representative average than measuring only a very short journey.
Why Dashboard Fuel Economy Can Differ
A vehicle’s onboard computer may estimate fuel consumption using engine and fuel-system data. A manual tank-to-tank calculation uses the distance traveled and the fuel quantity recorded during refueling. The two figures may not always match exactly.
Differences can result from measurement accuracy, fuel-pump cutoff, odometer variation, rounding, driving conditions and how the vehicle’s computer estimates fuel consumption.
What Affects Real-World Fuel Economy?
Fuel economy is not a fixed number under every driving condition. Actual consumption can change because of:
- Stop-start traffic and extended idling.
- Frequent hard acceleration or braking.
- Vehicle speed, particularly sustained high-speed driving.
- Passenger, luggage or cargo weight.
- Towing trailers or carrying roof loads.
- Tyre pressure and tyre condition.
- Air-conditioning and electrical accessory use.
- Hills, road surfaces, wind and weather.
- Engine condition and vehicle maintenance.
Comparing Two Vehicles
Fuel-economy figures are easier to compare when both vehicles are expressed in the same unit. This calculator displays all four units, so you can convert a recorded result before comparing it with another vehicle.
For MPG or km/L comparisons, the direction is reversed: the higher figure represents more distance traveled for each unit of fuel.
From Fuel Economy to Trip Cost
Fuel economy tells you how efficiently the vehicle uses fuel, but it does not by itself tell you how much a future journey will cost. For that, combine fuel economy with trip distance and fuel price.
Once you know your vehicle’s typical economy, use the Fuel Cost Calculator to estimate the fuel required and cost for a future journey.
You can also use the Speed, Distance & Time Calculator for related travel calculations.
Common Uses for a Fuel Economy Calculator
- Calculate actual fuel economy after refueling.
- Track changes in vehicle efficiency over time.
- Compare fuel consumption between vehicles.
- Convert metric fuel economy to MPG.
- Convert MPG-style measurements into metric equivalents.
- Review fleet or business vehicle fuel records.
- Create a realistic fuel figure for future trip-cost estimates.
Important: This calculator converts the distance and fuel values you enter mathematically. Real-world fuel economy can vary between trips and driving conditions. For a useful long-term vehicle average, compare multiple refueling records rather than relying on a single short trip.
Fuel Economy Calculator FAQs
How do I calculate fuel economy?
Measure the distance traveled and fuel consumed over the same period. For L/100 km, divide liters used by kilometers traveled and multiply by 100. Other units such as km/L and MPG express the same efficiency in a different format.
How much is 40 liters over 500 km in L/100 km?
40 ÷ 500 × 100 equals 8 L/100 km. The same efficiency is approximately 12.5 km/L, 29.4 US MPG and 35.3 UK MPG.
Is lower L/100 km better?
Yes. L/100 km measures the amount of fuel consumed to travel 100 kilometers, so a lower number indicates lower fuel consumption for the same distance.
Is higher MPG better?
Yes. MPG measures how many miles are traveled per gallon. A higher MPG figure therefore represents more distance traveled for each gallon of fuel.
What is the difference between US MPG and UK MPG?
US MPG uses a US gallon, while UK MPG uses an Imperial gallon. A US gallon is about 3.785 liters and an Imperial gallon is about 4.546 liters, so the two MPG numbers are different for the same vehicle efficiency.
Can I enter distance in miles?
Yes. Select miles beside the distance field. ToolZippy converts the distance internally and displays the resulting fuel economy in L/100 km, km/L, US MPG and UK MPG.
Can I enter fuel in gallons?
Yes. Fuel can be entered in liters, US gallons or UK/Imperial gallons. Make sure you select the correct gallon type because their volumes are different.
Why is my calculated economy different from the dashboard?
Dashboard readings and tank-to-tank calculations can differ because of estimation methods, fuel-pump cutoff, measurement accuracy, odometer variation and rounding. Driving conditions can also change between measurement periods.
How can I get a more representative fuel economy figure?
Record distance and fuel use across several refueling cycles and compare the combined values. A longer measurement period usually reduces the effect of one unusually efficient or inefficient trip.