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 Г· mpg | 25 mpg = 9.41 L/100km |
| L/100km | mpg US | 235.215 Г· L/100km | 8 L/100km = 29.4 mpg |
| mpg US | km/L | mpg Г— 0.425 | 25 mpg = 10.63 km/L |
| km/L | mpg US | km/L Г— 2.352 | 10 km/L = 23.5 mpg |
| mpg US | mpg UK | mpg Г— 1.201 | 25 mpg US = 30 mpg UK |
| mpg UK | mpg US | mpg Г— 0.833 | 30 mpg UK = 25 mpg US |
| km/L | L/100km | 100 Г· km/L | 12 km/L = 8.33 L/100km |
| L/100km | km/L | 100 Г· 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.