Fuel Efficiency — Volume Converter
Convert between volume-based fuel efficiency units — km/L, mi/gal (US/UK), L/100km, and more — instantly. Real-time conversion with copy-to-clipboard.
Fuel Efficiency — Volume Converter
Enter a value in any unit — see the conversion in all others instantly.
How to Use the Fuel Efficiency - Volume Converter
You are comparing two cars — a European model rated at 5.8 L/100km and a Japanese import rated at 17.2 km/L. The numbers look completely different but they describe the same thing. Enter either value and this converter shows both cars in the same unit so you can compare them directly. Nine volume-based fuel economy units are supported, covering metric, US, and UK standards.
A German sedan lists 6.2 L/100km on the window sticker. An American counterpart advertises 38 mpg US. Enter 6.2 in L/100km and the converter shows it equals 37.9 mpg US — nearly identical efficiency. The tool also shows 45.5 mpg UK, which explains why British car ads sometimes look more impressive than American ones.
A logistics company operates vehicles across the US and Europe. US trucks report gallons per 100 miles while European trucks report L/100km. Enter 12 gal/100mi and the converter shows 20.1 L/100km, giving the fleet manager a single metric to compare fuel costs across both continents.
A customer complains their car used to achieve 9.5 km/L but now only manages 7.8 km/L. Enter both values to see the change in L/100km: from 10.5 to 12.8 L/100km. That is a 22 percent increase in consumption, which points to a tune-up issue rather than normal driving variation.
A UK-market car shows 52 mpg UK on the dashboard. The US Customs form requires mpg US. Enter 52 in mpg UK and the result shows 43.3 mpg US. The 20 percent difference comes from the imperial gallon being larger than the US gallon — 4.546 litres versus 3.785 litres.
How the Fuel Efficiency - Volume Converter Works
The converter normalises all inputs to kilometers per litre (km/L) as the common intermediate, then converts from km/L to each target unit. Inverted units like L/100km are handled with a reciprocal calculation.
Distance-Per-Volume Units
Kilometres per litre (km/L) is the base unit. Miles per litre (mi/L) equals 0.621371 km/L. Miles per US gallon (mpg US) equals 2.35215 km/L because one US gallon holds 3.785 litres. Miles per UK gallon (mpg UK) equals 2.82481 km/L because the imperial gallon holds 4.546 litres. Higher values always mean better efficiency — the vehicle travels farther on the same volume of fuel.
Volume-Per-Distance Units
Units like L/100km and gal/100mi are mathematical inverses. To convert from 7 L/100km to km/L, the tool computes 100 / 7 = 14.286 km/L. The converter stores an inverted flag for these units and applies the reciprocal automatically. For gal/100mi, the tool first converts to L/100km using the appropriate gallon-to-litre factor, then applies the reciprocal to get km/L.
US vs UK Gallon Difference
The US gallon is defined as 231 cubic inches (3.785 litres) while the imperial gallon is 4.546 litres — about 20 percent larger. This means 50 mpg UK is only about 41.6 mpg US for the same actual fuel consumption. The converter stores separate factors for each gallon variant so you get accurate results without manually adjusting for the 1.20095 ratio.
Frequently Asked Questions
What is the difference between mpg US and mpg UK?
A US gallon contains approximately 3.785 liters, while a UK imperial gallon contains approximately 4.546 liters. Because the imperial gallon is larger, the same vehicle will show a higher mpg UK number than mpg US for the same actual fuel consumption. UK mpg figures are roughly 20 percent higher than their US equivalent.
How do I compare L/100km with mpg?
You cannot compare them directly because they measure opposite things — L/100km is a volume-per-distance metric where lower is better, while mpg is a distance-per-volume metric where higher is better. Use this converter to translate between them. For example, 7 L/100km equals about 33.6 mpg US or 40.4 mpg UK.
Why is a lower L/100km value better?
L/100km tells you how many liters of fuel the vehicle consumes to travel 100 kilometers. A car that uses 5 liters to cover 100 km is more efficient than one that uses 8 liters. Therefore, the lower the L/100km number, the less fuel the vehicle needs per unit of distance, which means better fuel economy.
Which fuel economy unit should I use?
Use the unit standard in your region. L/100km is the official metric in most of Europe, Asia, and Oceania. mpg US is the standard in the United States, while mpg UK is used in the United Kingdom. If you are comparing vehicles across regions, convert them all to the same unit using this tool for an accurate side-by-side comparison.
What are gal/100mi and how do they relate to L/100km?
gal/100mi is the US or UK gallon equivalent of L/100km — it measures fuel consumed per fixed distance. Just as L/100km tells you liters used per 100 km, gal/100mi tells you gallons used per 100 miles. Both are volume-per-distance metrics where lower values indicate better fuel efficiency. This converter supports both US and UK gallon variants.
Are the conversions in this tool accurate?
Yes. The tool uses standard conversion factors between gallons and liters and applies exact reciprocal math for inverted units. All calculations run in your browser with no rounding errors introduced by external APIs. The results are accurate to the precision of JavaScript floating-point arithmetic.