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Fuel Economy Studio
Vehicle Fuel Efficiency Calculator
Calculate real fuel economy from a fill-up, convert every major efficiency unit, project fuel costs and emissions, and compare two vehicles in one clear dashboard.
Metric, US and UK unitsCalculate from distance and fuel used
Choose the measurement system used by your odometer and fuel receipt. The calculator keeps US and Imperial gallons separate.
Your real-world fuel economy
Fuel use at a glance
Metric consumption—
Distance per litre—
US miles per gallon—
UK miles per gallon—
Trip fuel cost—
Cost per 100 km—
Cost per 100 miles—
Estimated full-tank range—
Estimated annual fuel—
Estimated annual fuel cost—
Estimated annual tailpipe CO₂—
Consumption scale
lower usehigher use
This passenger-car guide is only a broad reference. Vehicle size, load, weather, road and traffic conditions affect a fair comparison.
Fuel cost projection
This trip—
Per month—
Per year—
Calculation assumptions: Annual projections use the same measured fuel economy and fuel price. Range assumes the full usable tank capacity. Tailpipe CO₂ is an estimate and excludes fuel production and vehicle manufacturing.
Compare the running cost of two vehicles
Enter each vehicle’s published or measured consumption in the same unit. Lower L/100 km is better; higher MPG or km/L is better.
Vehicle comparison
Annual difference
Fuel saved per year—
Money saved per year—
Tailpipe CO₂ difference—
Consumption change—
Estimated payback period—
Current annual cost—
Alternative annual cost—
Calculation assumptions: Annual projections use the same measured fuel economy and fuel price. Range assumes the full usable tank capacity. Tailpipe CO₂ is an estimate and excludes fuel production and vehicle manufacturing.
Fuel economy formulas
For metric consumption, divide litres used by kilometres travelled and multiply by 100. MPG divides miles by gallons. US and Imperial gallons are different, so the two MPG values must not be mixed.
L/100 km = litres used ÷ kilometres travelled × 100
US MPG = miles travelled ÷ US gallons used
UK MPG = miles travelled ÷ Imperial gallons used
Reliable unit conversions: The calculator converts every result through litres per 100 kilometres. One US gallon is 3.785411784 litres; one Imperial gallon is 4.54609 litres; one mile is 1.609344 kilometres.
How to measure real fuel economy
Use the full-tank method
Fill the tank, reset the trip counter, drive normally, refill to the same level, then divide the travelled distance by the fuel added.
Measure several fill-ups
A single trip can be distorted by traffic, weather, short journeys or an uneven fill. Average several complete tanks for a more representative value.
Keep the units consistent
Enter kilometres with litres, miles with US gallons, or miles with Imperial gallons. Never treat US and UK gallons as the same volume.
Compare like with like
Vehicle size, passenger load, tyre type, road speed and climate control all influence consumption. Compare vehicles under similar conditions.
Check tyre pressure
Use the vehicle manufacturer’s cold-tyre recommendation. Incorrect pressure can increase fuel use and tyre wear.
Treat dashboard values as estimates
On-board computers can differ from pump-based calculations. The full-tank method is useful for checking the displayed average.
Typical passenger-car guide
These broad bands help interpret an L/100 km result; they are not a rating for every vehicle class.
Below 5 L/100 kmVery efficient for a conventional passenger car
5–7 L/100 kmEfficient to typical compact-car range
7–9 L/100 kmTypical mixed-use consumption
9–12 L/100 kmHigher consumption, common for larger or heavier vehicles
Above 12 L/100 kmVery high consumption; check vehicle class and driving conditions
Vehicle Fuel Efficiency Calculator FAQ
What is the difference between fuel economy and fuel consumption?
Fuel economy describes distance per unit of fuel, such as MPG or km/L, where a higher number is better. Fuel consumption uses fuel per distance, such as L/100 km, where a lower number is better.
Are US MPG and UK MPG the same?
No. An Imperial gallon is larger than a US gallon, so the same vehicle has a numerically higher UK MPG. This calculator reports them separately.
How can I calculate accurate real-world consumption?
Use the full-tank method across several fill-ups. Record the distance since the previous full tank and the amount added at the next full tank.
Why is my real fuel economy worse than the official figure?
Official tests use controlled procedures. Traffic, temperature, short trips, speed, load, tyres, terrain and climate control can all increase real-world fuel use.
How is annual fuel cost estimated?
The calculator applies the measured consumption to the annual distance and multiplies the required fuel by the price entered in the selected unit system.
Does the CO₂ result include the full environmental impact?
No. It estimates tailpipe CO₂ from fuel burned. It does not include extraction, refining, transport, electricity generation or vehicle manufacturing.