Fuel Economy Converter
Switch between mpg, km/L, and L/100km — works with both US and UK gallons. You can also compare two vehicles side by side or figure out what a trip will cost in gas.
Pick a tab, enter your numbers, and hit Convert.
Conversion Formulas
| From | To | Formula | Example |
|---|---|---|---|
| mpg US | L/100km | 235.215 ÷ mpg | 25 mpg = 9.41 L/100km |
| L/100km | mpg US | 235.215 ÷ L/100km | 8 L/100km = 29.4 mpg |
| mpg US | km/L | mpg × 0.425 | 25 mpg = 10.63 km/L |
| km/L | mpg US | km/L × 2.352 | 10 km/L = 23.5 mpg |
| mpg US | mpg UK | mpg × 1.201 | 25 mpg US = 30 mpg UK |
| mpg UK | mpg US | mpg × 0.833 | 30 mpg UK = 25 mpg US |
| km/L | L/100km | 100 ÷ km/L | 12 km/L = 8.33 L/100km |
| L/100km | km/L | 100 ÷ L/100km | 8 L/100km = 12.5 km/L |
- Divide 235 by mpg to get L/100km (and vice versa)
- For km/L, multiply mpg by 0.425
- UK gallons hold 20% more than US gallons
- Higher mpg means lower L/100km
US vs UK Gallons
| Measure | US | UK (Imperial) | Difference |
|---|---|---|---|
| 1 Gallon | 3.785 L | 4.546 L | UK is 20% larger |
| 25 mpg | 9.41 L/100km | 7.84 L/100km | Same car, different numbers |
UK ratings look higher because their gallons are bigger. A car rated 25 mpg in the US shows 30 mpg on UK sites. Same car, same efficiency, different number. Check which gallon type before comparing.
Fuel Economy Ranges
| Vehicle Type | mpg US | L/100km | km/L | Efficiency |
|---|---|---|---|---|
| Sports Car / Large Truck | 15-20 | 12-16 | 6-8 | Poor |
| Large SUV | 18-22 | 11-13 | 8-9 | Below Average |
| Mid-Size SUV | 22-28 | 8-11 | 9-12 | Average |
| Mid-Size Sedan | 25-32 | 7-9 | 11-14 | Good |
| Compact Car | 30-38 | 6-8 | 13-16 | Very Good |
| Hybrid | 45-55 | 4-5 | 19-23 | Excellent |
| Electric (MPGe) | 100-140 | 1.7-2.4 | 42-59 | Outstanding |
How Fuel Economy Numbers Work
Fuel economy can be expressed as distance per unit of fuel or fuel used per distance. MPG and km/L measure how far a vehicle travels on a gallon or liter, so higher numbers are better. L/100km measures fuel consumption, so lower numbers are better. The two styles are inverses.
The inverse relationship makes fuel savings less obvious in MPG. Moving from 15 to 20 mpg saves more fuel than moving from 35 to 40 mpg, even though both are 5 mpg improvements. L/100km can be easier for cost comparisons because it directly shows consumption.
Why Different Countries Use Different Units
The United States kept MPG because the road and fuel systems already used miles and gallons. Canada and most other countries use metric fuel consumption, commonly L/100km.
The UK mixes systems: fuel pumps sell liters, road signs show miles, and car efficiency is often reported in MPG using imperial gallons. Since imperial gallons are about 20 percent larger than US gallons, UK MPG is higher than US MPG for the same fuel consumption.
US vs UK Gallons
A US gallon is 3.785 liters. A UK gallon is 4.546 liters, about 20 percent more. That means 30 MPG in UK units is about 25 MPG in US units. When comparing cars across countries, check which gallon the spec sheet uses.
Electric Vehicle Efficiency
EVs do not burn gasoline, so MPGe compares electric energy use against the energy content of a gallon of gasoline. New EVs commonly rate much higher than gasoline cars on MPGe, but the more practical owner metric is often Wh per mile or kWh per 100 miles.
Electric efficiency can change with speed, temperature, terrain, tire choice, and cabin heating or cooling. Cold weather often raises energy use because the battery and cabin need heat.
The calculator above handles MPGe conversions too.
Factors Affecting Fuel Economy
Official ratings are controlled estimates, not guarantees. Gas cars often do better on steady highways where braking is limited. Hybrids often perform better in city traffic because regenerative braking recovers some energy.
Other factors that reduce mileage:
- Low tire pressure wastes gas
- Faster speeds burn more fuel, especially above 50 mph
- Extra weight in the car or cargo area
- Running the AC or heater
- Roof racks add drag even when they're empty
- Aggressive driving, including hard acceleration and braking
Doing the Math
The basic trip-cost math is miles divided by MPG to get gallons, then gallons multiplied by fuel price to get cost. A 300-mile trip at 25 MPG and $3.50 per gallon costs about $42.
The vehicle comparison tab applies the same math over a year. Compare the current vehicle against another option to estimate annual fuel savings. For the energy content behind fuel and electricity comparisons, the energy converter can compare kWh, MJ, BTU, and gasoline-equivalent energy.
Common Questions
How do you convert MPG to L/100km? For US MPG, divide 235.214 by MPG.
How do you convert L/100km to MPG? For US MPG, divide 235.214 by L/100km.
Are US MPG and UK MPG the same? No. UK imperial gallons are larger, so UK MPG appears higher for the same vehicle.
Using Fuel Economy Converter for one defined quantity
Fuel Economy Converter compares several fuel economy units without changing the underlying measured quantity. Use one source value from one vehicle and operating case with a defined distance, fuel-volume convention, and average consumption period.
This broader hub is useful for vehicle records, trip planning, fleet comparisons, and international specifications. Within Fuel Economy Converter, select the actual source and destination labels before interpreting the numerical difference; a familiar abbreviation is not evidence that the correct unit was selected.
Within Fuel Economy Converter, the converter performs arithmetic from the entered value and selected units. Within Fuel Economy Converter, it does not measure the source, identify its standard, inspect its context, or decide how much precision the destination record supports.
Source records for fuel economy
Confirm US or Imperial gallons and distinguish distance per volume from volume per distance. Reciprocal fuel-consumption scales require more than a simple multiplier.
Write the source number and unit together before opening Fuel Economy Converter. Within Fuel Economy Converter, after conversion, retain the destination symbol beside the answer and keep the original entry available for review.
Within Fuel Economy Converter, if multiple records use different units, convert each row to one agreed destination before adding, averaging, sorting, or comparing thresholds. Within Fuel Economy Converter, do not edit the source column into an unlabeled mixture.
Checking the selected unit path
Rebuild distance and fuel volume separately, then calculate both miles per gallon and liters per 100 kilometers from the same trip.
Within Fuel Economy Converter, an inverse conversion should recover the source within rounding. Within Fuel Economy Converter, a second route is stronger when it uses a base unit or independently derived relationship rather than the same selected menus and value.
Within Fuel Economy Converter, test a simple benchmark such as zero, one source unit, or a known reference quantity. Within Fuel Economy Converter, for reciprocal or offset relationships, use the governing equation instead of assuming that doubling always behaves like a zero-offset multiplier.
Precision, limits, and related conversions
Important boundaries for Fuel Economy Converter include US versus Imperial gallons, reciprocal scales, driving cycle, weather, load, idling, charging or fuel losses, and tank-fill measurement error. Within Fuel Economy Converter, keep the boundary that applies to the source record beside the converted answer.
Within Fuel Economy Converter, round after the final required conversion, not at every intermediate menu change. Within Fuel Economy Converter, the source measurement limits the defensible significant digits even when the interface displays a longer decimal.
For focused follow-up calculations from Fuel Economy Converter, open Miles To Kilometers Converter, Gallons To Liters Converter and Liters Per Minute To Gallons Per Minute Converter. These linked pages keep the fuel economy source and destination visible and provide an inverse check for their specific unit pair.
Questions about Fuel Economy Converter
How many digits should be reported?
FAQ guidance for Fuel Economy Converter: carry guard digits through later arithmetic, then round to the resolution supported by the source measurement and destination use. FAQ guidance for Fuel Economy Converter: extra display digits are not extra measurement accuracy.
Can values from different units be totaled?
FAQ guidance for Fuel Economy Converter: only after all entries represent the same physical quantity and have been converted to one shared unit. FAQ guidance for Fuel Economy Converter: retain the original unit in a separate column for traceability.