Fuel Efficiency Converter | All Units
Convert fuel efficiency between L/100km, MPG US, MPG UK, km/L, gal/100mi, and mi/L simultaneously. Includes efficiency rating and vehicle class comparison.
Quick presets
What Is the Fuel Efficiency Converter | All Units?
Fuel efficiency describes how far a vehicle travels per unit of fuel consumed. The frustrating reality is that every major market uses a different unit, and two of the most common (MPG and L/100km) are inversely related, meaning “higher is better” for one and “lower is better” for the other. This converter handles all six major units and displays every result simultaneously so you can compare any two systems at a glance.
All conversions pass through L/100km as a common base. The efficiency rating (Excellent / Good / Average / Poor / Very poor) is based on US MPG thresholds: 50+ MPG is Excellent, 35+ is Good, 25+ is Average, 18+ is Poor, below 18 is Very poor. These ratings reflect modern passenger vehicle expectations and do not apply to commercial vehicles.
All calculations run entirely in your browser, no data is sent to any server.
Formula
How to Use
- 1Enter your efficiency value: Type the fuel economy figure from your car's manual, instrument cluster, or fuel receipt into the input field.
- 2Select the input unit: Choose the unit that matches your entered value: L/100km, MPG (US), MPG (UK), km/L, gal/100mi, or mi/L.
- 3Read all conversions: All six unit conversions update instantly. No Calculate button needed, results appear as you type.
- 4Check the efficiency rating: An orange banner shows your efficiency rating from Excellent to Very poor, based on the US MPG equivalent.
- 5Compare to vehicle classes: The vehicle comparison table shows how your figure compares to typical hybrid, compact, sedan, SUV, pickup, sports car, and bus values.
- 6Use quick presets: Click a preset (Toyota Prius, Average sedan, Large SUV, etc.) to see where a benchmark vehicle sits across all six units.
- 7Expand step-by-step: Click "Step-by-step conversion" to see each formula applied with your actual value, useful for learning or verification.
- 8Use for trip planning: Once you know your L/100km equivalent, use the Fuel Cost Calculator to compute exact trip costs in any currency.
Example Calculation
Example 1, European car at 6 L/100km
Input: 6 L/100km
MPG (US) = 235.215 / 6 = 39.2 MPG
MPG (UK) = 282.481 / 6 = 47.1 MPG
km/L = 100 / 6 = 16.67 km/L
gal/100mi = 6 / 2.352 = 2.55 gal/100mi
Rating: Good (39 MPG US)
Example 2, US truck at 18 MPG (US)
Input: 18 MPG US
L/100km = 235.215 / 18 = 13.07 L/100km
MPG (UK) = 282.481 / (235.215/18) = 21.6 MPG UK
km/L = 100 / 13.07 = 7.65 km/L
Rating: Poor (18 MPG US is at the Poor threshold)
Example 3, Japanese kei car at 20 km/L
Input: 20 km/L
L/100km = 100 / 20 = 5.0 L/100km
MPG (US) = 235.215 / 5.0 = 47.0 MPG
MPG (UK) = 282.481 / 5.0 = 56.5 MPG
Rating: Excellent
Understanding Fuel Efficiency Converter | All Units
Why Fuel Efficiency Units Are Confusing
The global lack of a single fuel efficiency standard creates confusion whenever you compare vehicles across markets. A European manufacturer quoting 5 L/100km and a US manufacturer quoting 47 MPG are describing essentially the same vehicle efficiency , but the numbers bear no obvious mathematical relationship without conversion.
The most counterintuitive aspect is the inverse relationship between consumption-based (L/100km, gal/100mi) and distance-based (MPG, km/L) metrics. A 1 L/100km improvement from 10 to 9 L/100km saves 125% more fuel per 10,000 km than a 1 MPG improvement from 40 to 41 MPG, even though both are a single-unit change. This asymmetry makes L/100km more useful when comparing real fuel savings.
Vehicle Class Benchmarks
| Vehicle type | Typical L/100km | MPG (US) | Rating |
|---|---|---|---|
| Small hybrid / EV | 4.4 | 53 | Excellent |
| Compact hatchback | 5.9 | 40 | Good |
| Average sedan | 7.8 | 30 | Average |
| Crossover SUV | 8.7 | 27 | Average |
| Large SUV / minivan | 10.7 | 22 | Poor |
| Full-size pickup truck | 11.8 | 20 | Poor |
| Sports car | 9.4 | 25 | Average |
| City bus (per passenger) | 39.2 | 6 | Very poor (per vehicle) |
Frequently Asked Questions
Why does the UK get better MPG than the US for the same car?
The UK MPG figure is always numerically higher because it uses the larger Imperial gallon (4.546 L) rather than the US gallon (3.785 L).
- • UK gallon = 4.546 L • US gallon = 3.785 L
- • Conversion: MPG (US) = MPG (UK) × 0.8327
- • A car quoted at 50 MPG (UK) = only 41.6 MPG (US)
Always check which gallon a fuel economy figure refers to when comparing international sources.
What is the inverse relationship between MPG and L/100km?
MPG measures how far you travel per unit of fuel (higher = more efficient). L/100km measures how much fuel you use per unit of distance (lower = more efficient). They are reciprocals.
This creates a counterintuitive effect: improving from 15 to 20 MPG saves 1.57 L/100km; improving from 40 to 45 MPG saves only 0.65 L/100km, despite both being a 5 MPG improvement.
What is MPGe and how is it shown here?
MPGe (miles per gallon equivalent) is the US EPA measure for electric and plug-in hybrid vehicles. It treats 33.7 kWh of electricity as equivalent to one US gallon of gasoline.
- • A Tesla Model 3 Long Range: ~134 MPGe
- • This converter works with MPGe exactly like MPG (US)
- • Real-world range varies significantly with temperature and driving style
What is the gal/100mi unit?
Gallons per 100 miles is an American variant of L/100km, using US gallons and miles instead of litres and kilometres. Like L/100km, lower is better.
It was proposed as a clearer alternative to MPG because it makes efficiency improvements more intuitive (same inverse-relationship problem as MPG vs L/100km).
How accurate are official fuel efficiency ratings?
Official ratings (EPA, WLTP, NEDC) are measured on standardized test cycles and typically overestimate real-world efficiency by 5–30%:
- • WLTP (Europe, post-2017): most realistic; typically 10–15% optimistic
- • EPA (US): reasonable for highway; city estimates can be 20% optimistic
- • NEDC (older European standard): notoriously up to 30% off real-world
For trip budgeting, use your own measured consumption from previous fill-ups rather than the official rating.
How do I find my car's actual fuel efficiency?
The most accurate method is to measure it yourself:
- 1. Fill the tank completely. Reset the trip odometer.
- 2. Drive normally until you need refuelling.
- 3. Fill the tank completely again. Note litres added and km driven.
- 4. L/100km = litres ÷ km × 100
Repeat over several fill-ups for a reliable average that accounts for seasonal and route variation.
What is the efficiency rating scale used here?
The rating is based on US MPG for modern passenger vehicles:
- • Excellent: 50+ MPG (4.7 L/100km), hybrids, small EVs
- • Good: 35–50 MPG (4.7–6.7 L/100km), efficient compacts
- • Average: 25–35 MPG (6.7–9.4 L/100km), typical sedans
- • Poor: 18–25 MPG (9.4–13.1 L/100km), large SUVs, trucks
- • Very poor: below 18 MPG, heavy trucks, sports cars, old vehicles
Does driving style affect fuel efficiency significantly?
Driving style is one of the largest controllable factors, typically accounting for 15–30% variation in real-world consumption:
- • Smooth acceleration and anticipatory braking: biggest single factor
- • Maintaining steady speed (cruise control on highways): 5–10% saving
- • Reducing highway speed from 130 to 110 km/h: 15–20% saving
- • Correct tyre pressure: 1–3% saving