Understanding Fuel Consumption: MPG vs L/100km
A practical guide to understanding and converting between the world's two main fuel consumption metrics — miles per gallon and liters per 100 kilometers.
Last updated: 2025-03-15
Introduction: Two Ways to Measure Fuel Economy
Fuel economy is measured differently depending on where you are. The United States uses miles per gallon (MPG) — how far you can drive on one gallon of fuel. Most of the rest of the world uses liters per 100 kilometers (L/100km) — how much fuel you need to travel 100 km. These two metrics work in opposite directions: a higher MPG number means better efficiency, while a lower L/100km number means better efficiency. This inverse relationship makes direct comparison confusing without conversion. This guide gives you the formulas, worked examples, and practical context to convert between them confidently.
The Conversion Formulas
Because the relationship is inverse (not linear), you cannot simply multiply by a fixed number. Instead:
- US MPG to L/100km: L/100km = 235.215 ÷ US MPG
- L/100km to US MPG: US MPG = 235.215 ÷ L/100km
- Imperial (UK) MPG to L/100km: L/100km = 282.481 ÷ UK MPG
- L/100km to Imperial MPG: UK MPG = 282.481 ÷ L/100km
- US MPG to UK MPG: UK MPG = US MPG × 1.20095
The magic numbers 235.215 and 282.481 come from the exact conversion factors between miles, kilometers, gallons, and liters.
Worked Examples
Example 1: Converting 30 US MPG to L/100km
235.215 ÷ 30 = 7.84 L/100km. A car getting 30 MPG in the US would be rated at about 7.8 L/100km in Europe — good efficiency for a mid-size sedan.
Example 2: Converting 6.5 L/100km to US MPG
235.215 ÷ 6.5 = 36.19 US MPG. A European car rated at 6.5 L/100km would achieve about 36 MPG on the US scale — an efficient compact car.
Example 3: Converting 45 UK MPG to US MPG
UK gallons are larger than US gallons, so UK MPG figures are higher. 45 UK MPG ÷ 1.20095 = 37.47 US MPG. Alternatively, in L/100km: 282.481 ÷ 45 = 6.28 L/100km.
Fuel Economy Reference Chart
| US MPG | UK MPG | L/100km | Vehicle Type |
|---|---|---|---|
| 15 | 18.0 | 15.68 | Large truck / SUV |
| 20 | 24.0 | 11.76 | Full-size SUV |
| 25 | 30.0 | 9.41 | Mid-size sedan |
| 30 | 36.0 | 7.84 | Efficient sedan |
| 35 | 42.0 | 6.72 | Compact car |
| 40 | 48.0 | 5.88 | Efficient compact / diesel |
| 50 | 60.0 | 4.70 | Hybrid |
| 60 | 72.0 | 3.92 | Plug-in hybrid |
Why the Inverse Relationship Matters
The inverse relationship between MPG and L/100km has an important practical consequence: improvements at the low end of the MPG scale save more fuel than improvements at the high end. Upgrading from 10 MPG to 15 MPG saves far more fuel than upgrading from 30 MPG to 35 MPG over the same distance. In L/100km, this is more intuitive: going from 23.5 to 15.7 L/100km (a 7.8 L drop) saves much more than going from 7.8 to 6.7 L/100km (a 1.1 L drop). This is one reason many economists argue that L/100km is a better metric for evaluating fuel savings.
Real-World Applications
- Car shopping: When comparing vehicles across US and European markets, converting between MPG and L/100km lets you make apples-to-apples comparisons.
- Travel planning: Renting a car abroad? Understanding the local fuel economy metric helps you budget for gas.
- Environmental comparisons: CO₂ emissions correlate directly with fuel consumption. L/100km gives a more linear relationship to emissions than MPG.
- Fleet management: Companies operating vehicles internationally need to standardize fuel efficiency reporting.
Use our fuel consumption converter for instant conversions between MPG, L/100km, and other fuel economy units.
Frequently Asked Questions
How do I convert MPG to L/100km?
Divide 235.215 by the US MPG value. For example, 30 MPG = 235.215 ÷ 30 = 7.84 L/100km. For UK (Imperial) MPG, divide 282.481 by the MPG value instead.
Why are MPG and L/100km inverse of each other?
MPG measures distance per unit of fuel (higher is better), while L/100km measures fuel per unit of distance (lower is better). They are reciprocals, so as one increases, the other decreases.
Is US MPG the same as UK MPG?
No. A US gallon is 3.785 liters, while an Imperial (UK) gallon is 4.546 liters. UK MPG figures are about 20% higher than US MPG for the same vehicle. A car rated at 30 US MPG would be rated at about 36 UK MPG.
What is good fuel economy in L/100km?
For a modern passenger car, 5-7 L/100km (34-47 US MPG) is considered good. Hybrids achieve 3-5 L/100km (47-78 US MPG). SUVs and trucks typically use 8-13 L/100km (18-29 US MPG).