Understanding Fuel Economy Conversions

Fuel economy conversion is essential for comparing vehicle efficiency across different regions, understanding fuel costs when traveling internationally, and evaluating vehicle specifications from different manufacturers. The US uses MPG (miles per gallon), while most other countries use L/100km (liters per 100 kilometers).

Fuel Economy Units Explained

Unit	Used In	Meaning	Better = Higher/Lower
MPG (US)	United States	Miles traveled per US gallon	Higher is better
MPG (UK)	United Kingdom	Miles traveled per imperial gallon	Higher is better
L/100km	Europe, Canada, Australia	Liters consumed per 100 km	Lower is better
km/L	Asia, some other regions	Kilometers traveled per liter	Higher is better

Quick Conversion Reference

MPG (US)	MPG (UK)	L/100km	km/L
20	24	11.8	8.5
25	30	9.4	10.6
30	36	7.8	12.8
35	42	6.7	14.9
40	48	5.9	17.0
50	60	4.7	21.3

Why Different Gallons?

The US and UK use different gallon sizes, making MPG conversions confusing:

• US gallon: 3.785 liters (smaller)
• UK imperial gallon: 4.546 liters (larger, 20% more)
• Result: UK MPG numbers are ~20% higher than US MPG for the same vehicle
• Example: 30 US MPG = 36 UK MPG = 7.8 L/100km

Practical Applications

International Vehicle Comparison

When comparing vehicles across regions, conversions are essential. A European car advertised at 5.5 L/100km equals 43 US MPG - excellent fuel economy. Asian specifications in km/L need conversion for US buyers.

Travel Planning and Fuel Costs

Renting a car abroad requires understanding local fuel economy units. If a European rental shows 6.0 L/100km consumption, you'll use 6 liters per 100 kilometers traveled. At €1.50/liter, that's €9 per 100km ($10 per 62 miles).

Cost Comparison Calculator

Calculate fuel costs using conversions:

Environmental Impact

Fuel economy directly relates to CO2 emissions. Lower fuel consumption means lower emissions. A car using 8 L/100km produces about 184g CO2/km, while a 5 L/100km car produces about 115g CO2/km.

Typical Fuel Economy by Vehicle Type

Vehicle Type	MPG (US)	L/100km	Notes
Compact car	30-40	5.9-7.8	Good fuel economy
Mid-size sedan	25-35	6.7-9.4	Average efficiency
SUV/Crossover	20-28	8.4-11.8	Heavier, less efficient
Pickup truck	15-22	10.7-15.7	Lower fuel economy
Hybrid	45-55	4.3-5.2	Excellent efficiency
Electric (MPGe)	100-130	2.3-1.8	Equivalent measure

Understanding MPGe (Electric Vehicles)

Electric vehicles use MPGe (miles per gallon equivalent) to compare with gas cars:

• 1 gallon of gasoline = 33.7 kWh of energy
• A car using 33.7 kWh to travel 100 miles = 100 MPGe
• Tesla Model 3: ~130 MPGe (extremely efficient)
• Nissan Leaf: ~110 MPGe

Factors Affecting Fuel Economy

• Driving style: Aggressive acceleration/braking reduces efficiency 15-30%
• Speed: Highway driving over 50 mph reduces MPG significantly
• Tire pressure: Under-inflated tires reduce fuel economy 0.2% per PSI
• Weight: Extra 100 pounds reduces MPG by 1-2%
• AC usage: Can reduce fuel economy by 10-25% in city driving
• Weather: Cold weather reduces fuel economy due to engine warmup and denser air

Conversion Formulas

For manual calculations:

• US MPG to L/100km: 235.214 ÷ MPG
• L/100km to US MPG: 235.214 ÷ L/100km
• UK MPG to L/100km: 282.481 ÷ UK MPG
• L/100km to UK MPG: 282.481 ÷ L/100km
• US MPG to UK MPG: US MPG × 1.201
• km/L to L/100km: 100 ÷ km/L

Tips for Better Fuel Economy

• Maintain steady speed: Use cruise control on highways
• Reduce idling: Turn off engine if stopped over 30 seconds
• Proper maintenance: Regular oil changes, air filter replacement
• Remove excess weight: Clean out trunk and remove roof racks when not needed
• Combine trips: Multiple short trips use more fuel than one longer trip
• Plan routes: Avoid traffic and excessive stops