MPG vs L/100km vs km/L: Global Fuel Efficiency Units Explained & Converted

Published: October 3, 2025 7 min read 1,300 words

Understanding global fuel efficiency units enables accurate vehicle comparisons, international research, and travel planning across different measurement systems. This in-depth guide covers MPG, L/100km, and km/L conversions with practical applications for worldwide fuel economy analysis.

Instant conversions: Use our global calculator with automatic unit conversion for all international standards.

The three global systems

Three units dominate international fuel-economy reporting. MPG (miles per gallon) in the US and the UK, L/100km (liters per 100 kilometers) in Europe, Australia, and most of the rest of the world, and km/L in parts of Asia. Each asks a slightly different question. MPG answers "how far on a unit of fuel." L/100km answers "how much fuel for a fixed distance." km/L is the metric cousin of MPG and answers the same question in metric units.

The fuel mileage calculation guide works through the underlying math; this page is the conversion reference.

MPG (US/UK) — higher is better

  • Formula: distance (miles) ÷ fuel (gallons)
  • Where: United States, United Kingdom
  • Typical range: 15 to 50 MPG for passenger vehicles; 50+ MPG for hybrids

L/100km — lower is better

  • Formula: (fuel in liters × 100) ÷ distance (km)
  • Where: Europe, Australia, New Zealand, most international markets
  • Typical range: 4 to 15 L/100km for passenger vehicles

km/L — higher is better

  • Formula: distance (km) ÷ fuel (liters)
  • Where: Japan (historically), some Asian markets, motorcycle and small-engine applications worldwide
  • Typical range: 10 to 22 km/L for passenger vehicles

The conversion formulas

Reference constants

MPG (US) to L/100km: L/100km = 235.214583 ÷ MPG

L/100km to MPG (US): MPG = 235.214583 ÷ L/100km

MPG (US) to km/L: km/L = MPG × 0.425144

km/L to MPG (US): MPG = km/L ÷ 0.425144

MPG (UK) to MPG (US): MPG (US) = MPG (UK) × 0.833

The constant 235.214583 comes from 100 km ÷ 1.609344 miles × 3.785412 L/gallon, the same conversion used by every major automaker. The UK gallon (4.546 L) and the US gallon (3.785 L) are different, which is why a "40 MPG" UK figure is a "33 MPG" US figure for the same car. The math derivation is on the MPG formula math page.

Worked examples

Convert 30 MPG (US) to L/100km

L/100km = 235.214583 ÷ 30 = 7.84 L/100km

30 MPG (US) is "excellent" for a non-hybrid gas car. The European equivalent is 7.8 L/100km.

Convert 8.5 L/100km to MPG (US)

MPG = 235.214583 ÷ 8.5 = 27.7 MPG (US)

8.5 L/100km is "good" efficiency in European terms. The US equivalent is about 28 MPG.

Quick-reference table

MPG (US) L/100km km/L Efficiency rating
504.721.3Excellent
405.917.0Very good
307.812.8Good
259.410.6Average
2011.88.5Below average
1515.76.4Poor

Regional standards and the testing cycle behind the number

The unit is only half the story. The number on the sticker also depends on which test cycle was used to measure it. A car sold in the US, in Europe, and in Japan will carry three different ratings for the same engine, and the differences are not just rounding error.

Three test cycles dominate global fuel-economy reporting:

  • EPA (US): FTP-75 city, HWFET highway, SC03 (A/C), US06 (aggressive), and a cold-start procedure. Five cycles combined into a single "combined" rating.
  • WLTP (Europe and most of the world): Worldwide Harmonised Light Vehicles Test Procedure. Four phases (low, medium, high, extra-high speed) that span a wider range of driving conditions than the EPA procedure.
  • JC08 (Japan): The Japanese cycle through 2018. Japan has since transitioned to WLTP, so JC08 is mostly of historical interest for new vehicles. Some legacy ratings and motorcycle data are still reported against it.

The full comparison of the three cycles (test phases, durations, real-world correlation, and how to convert between them) is on the EPA vs WLTP vs JC08 guide. The short version: a US EPA rating of 30 MPG and a European WLTP rating of 7.8 L/100km for the same car are roughly equivalent, but neither is what you will measure on the road. Real-world MPG is typically 10 to 15 percent below the lab rating; the factors guide explains why.

International vehicle comparison

When comparing vehicles from different markets, the unit conversion is the easy part. The harder question is whether the test cycles are comparable. A US-spec Camry at 32 city / 42 highway / 36 combined MPG (EPA) and a European-spec Camry at 6.1 L/100km combined (WLTP) are within a few percent of each other, but they are not directly equivalent. The comparison calculator handles the unit conversion; the test-cycle difference is on you to research.

Working with mixed units in the wild

Three situations where you actually need this math in real life:

  • Travel or fleet operations across borders. A UK logistics company running a mix of European vans and American trucks needs to standardise on one unit for internal reporting. Most large fleets pick L/100km (it pairs naturally with European door-jamb labels) or MPG (US) (if the drivers and fuel cards are US-based). The dangerous mistake is mixing the two within a single comparison; an "MPG (UK) of 33 versus an L/100km of 9.0" is meaningless because the two numbers describe different vehicles under different standards.
  • Reading a non-native brochure or review. European and Japanese reviews report L/100km or km/L. Converting to MPG (US) before comparison is one line of math (the formulas above).
  • Calculating fuel cost across regions. Cost per mile and cost per kilometer are not interchangeable; the trip cost calculator does the conversion for you if you have the fuel price in either gallons or liters.

Why Two Countries Use Two Different Units

MPG and L/100km are not just different numbers, they are answers to different questions. Miles per gallon tells you how far you can travel on a unit of fuel. Litres per hundred kilometres tells you how much fuel you need to travel a fixed distance. The two metrics are mathematically reciprocal (after unit conversion), but psychologically they push in opposite directions. A higher MPG is better; a lower L/100km is better. This is why the same car, advertised on opposite sides of the Atlantic, can carry both a 30 MPG sticker and a 7.8 L/100km sticker without anyone being misleading.

The historical reason for the split is regulatory. The United States standardised on miles and US gallons (3.785 L) through the Energy Policy and Conservation Act of 1975, which made MPG the de-facto efficiency metric for CAFE compliance. Europe, Japan, and most of the rest of the world adopted the metric system earlier and used L/100km because it pairs naturally with the litre (the standard fuel-trade unit) and the kilometre (the standard distance unit). The UK's transition to L/100km in primary fuel-economy reporting is more recent, and UK drivers still encounter MPG in older marketing material; the conversion is complicated by the fact that the UK traditionally used imperial gallons (4.546 L) rather than US gallons, so a "UK MPG" of 40 corresponds to a "US MPG" of approximately 33.

Quick Reference Conversion Table

For a representative range of modern passenger vehicles. All conversions use the US gallon (3.785 L) unless explicitly noted; for the UK gallon, multiply MPG (US) by 0.833 to get MPG (UK).

Vehicle Class MPG (US) L/100km km/L
Compact sedan (e.g. Toyota Corolla hybrid)524.522.2
Mid-size SUV (e.g. Honda CR-V)288.411.9
Full-size pickup (e.g. Ford F-150 2.7L)2210.79.3
Hybrid sedan (e.g. Camry hybrid)465.119.6
Battery EV (e.g. Nissan Leaf, MPGe)1122.147.6

The Reciprocal Trap

A common mistake is to assume that halving L/100km doubles MPG. It does not. Because the two units are reciprocals, a 50% reduction in L/100km corresponds to a doubling of fuel efficiency per unit distance, which is the same as a doubling of MPG. But a 20% reduction in L/100km corresponds to a 25% increase in MPG, not a 20% increase. The asymmetry is small at high efficiencies (where the curve is approximately linear) and large at low efficiencies (where the curve bends). A car that goes from 5 MPG to 10 MPG has improved by 100% in MPG, but only by 50% in L/100km (from 47.0 to 23.5 L/100km). The two metrics tell the same story; they just bend differently.

Working With Mixed Units in Fleet Operations

If you operate a fleet that includes vehicles from both the metric and the imperial world, for example, a UK logistics company running a mix of European vans and American trucks, the safest practice is to pick one canonical unit for internal reporting and convert at the edges. Most large fleets standardise on L/100km because it is the unit the European OEMs use on the door-jamb labels, but if your drivers are American and your fuel cards report in US gallons, MPG (US) is the more practical choice. The important thing is to never mix the two within a single comparison; an "MPG (UK) of 33 versus an L/100km of 9.0" is meaningless because the two numbers describe different vehicles under different standards.