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Fuel Consumption Calculator

L/100km
8.0
MPG (US)
29.4
km/L
12.5
Cost/100km
$12
JT
James Taylor
Automotive Engineer
Updated: November 2025

Understanding Fuel Consumption Units

Different regions use different standards to measure fuel efficiency. The United States primarily uses MPG (Miles Per Gallon), while most of the world uses the metric system with L/100km (Liters Per 100 Kilometers).

MPG vs L/100km: The Key Difference

Measurement What It Measures Better = ?
MPG (US) Distance traveled per gallon of fuel Higher is better โ†‘
L/100km Liters of fuel used per 100 km Lower is better โ†“
km/L Kilometers traveled per liter of fuel Higher is better โ†‘

Fuel Economy by Vehicle Type

๐Ÿ’ก Expert Tip: The 55-65 MPH Sweet Spot

"Most vehicles achieve peak fuel efficiency between 55-65 mph. Every 5 mph over 60 mph is like paying an extra $0.20 per gallon. Aggressive driving (rapid acceleration and hard braking) can lower your gas mileage by 33% on highways and 5% in the city. Use cruise control on highways to maintain steady speed."

โ€” James Taylor, Automotive Engineer

โš ๏ธ Common Mistakes

  1. Confusing MPG Directions โ€” In MPG, higher is better (40 MPG is more efficient than 20 MPG). In L/100km, lower is better (5 L/100km is more efficient than 10 L/100km). Don't mix them up!
  2. Trusting EPA Ratings Blindly โ€” Lab-tested EPA ratings are typically 10-30% higher than real-world results. Factors like traffic, AC usage, cargo weight, tire pressure, and driving style significantly impact actual MPG.
  3. Using Imperial vs US Gallons โ€” UK MPG uses Imperial gallons (4.546 L), while US MPG uses US gallons (3.785 L). UK MPG is ~20% higher for the same car. Always check which standard you're using!
  4. Idling Wastes More Than You Think โ€” Idling for 10 seconds uses more fuel than restarting your engine (in modern vehicles). If you're stopped for more than 10 seconds, turn off the engine to save gas.

Quick Conversion Reference

MPG (US) L/100km km/L Efficiency
50 MPG 4.7 L/100km 21.3 km/L Excellent (Hybrid)
30 MPG 7.8 L/100km 12.8 km/L Good (Compact)
20 MPG 11.8 L/100km 8.5 km/L Average (SUV)
15 MPG 15.7 L/100km 6.4 km/L Poor (Truck)

Tips to Improve Fuel Economy

Frequently Asked Questions

What is considered good fuel economy?

Good fuel economy depends on vehicle type:

  • Compact cars: 30-40 MPG (7.8-5.9 L/100km)
  • Mid-size sedans: 25-35 MPG (9.4-6.7 L/100km)
  • SUVs: 20-30 MPG (11.8-7.8 L/100km)
  • Trucks: 15-25 MPG (15.7-9.4 L/100km)
  • Hybrids: 50+ MPG (under 4.7 L/100km)

How do I convert MPG to L/100km?

Formula: L/100km = 235.2 รท MPG

For example: 30 MPG = 235.2 รท 30 = 7.84 L/100km

Note that MPG measures distance per fuel (higher is better), while L/100km measures fuel per distance (lower is better).

Why is my actual MPG lower than EPA rating?

EPA ratings are tested in controlled lab conditions. Real-world MPG is typically 10-30% lower due to:

  • Aggressive driving (hard acceleration/braking)
  • Excessive idling
  • AC usage and cargo weight
  • Tire pressure and traffic conditions
  • Cold weather (reduces efficiency by 12-15%)

Highway driving usually gets closer to EPA estimates than city driving.

How can I improve my fuel economy?

Best practices to maximize MPG:

  • Maintain steady speed (cruise control on highway)
  • Avoid aggressive acceleration/braking
  • Keep tires properly inflated (+3% MPG)
  • Remove excess cargo weight
  • Avoid excessive idling (turn off if stopped 10+ seconds)
  • Combine trips (warm engine is more efficient)
  • Use recommended motor oil
  • Replace air filters
  • Drive at moderate speeds (55-65 mph is most efficient)