Conversion July 13, 2026 · 8 Min Read

MPG & Fuel Consumption Converter – Guide & Formulas

Calculate fuel economy in miles per gallon (MPG US and UK) and convert to metric units like L/100km or km/L instantly.

Calculate and convert vehicle fuel efficiency between global systems. Enter distance and fuel consumption to compute Miles Per Gallon (US and Imperial/UK), Liters per 100 Kilometers (L/100km), and Kilometers per Liter (km/L) instantly.

Key Takeaway

Use the free MPG & Fuel Consumption Converter to calculate fuel economy in miles per gallon (mpg us and uk) and convert to metric units like l/100km or km/l instantly. Get instant results with step-by-step explanations.

How to Use the MPG & Fuel Consumption Converter

  1. Enter the distance driven (in miles or kilometers).
  2. Input the fuel volume consumed (in US gallons, Imperial gallons, or Liters).
  3. Review the comprehensive fuel economy metrics comparing US MPG, UK MPG, L/100km, and km/L side-by-side.

The Formula

US MPG = Miles / US Gallons | UK MPG = Miles / Imperial Gallons (1 Imperial Gallon = 1.20095 US Gallons) | km/L = (Miles * 1.60934) / (US Gallons * 3.78541) | L/100km = 100 / (km/L)

Variable Definitions

  • L/100km: Liters of fuel consumed per 100 kilometers traveled (standard metric fuel consumption metric)
  • km/L: Kilometers traveled per single liter of fuel consumed
  • UK MPG: Miles per Imperial gallon, used in the United Kingdom and Commonwealth nations

Comparing US and Metric Fuel Efficiencies

A hybrid vehicle averages 45.0 Miles Per Gallon (US). Convert this fuel economy rating to Liters per 100 Kilometers (L/100km) and Kilometers per Liter (km/L) for European comparison.

  1. Step 1: Check the conversion factor between US MPG and L/100km: L/100km = 235.215 / US MPG.
  2. Step 2: Apply the formula: L/100km = 235.215 / 45.0 = 5.23 Liters consumed per 100 kilometers driven.
  3. Step 3: Calculate Kilometers per Liter (km/L): km/L = 100 / 5.23 ≈ 19.12 km/L.
  4. Step 4: A 45 MPG rating corresponds to 5.23 L/100km or 19.12 km/L.

Frequently Asked Questions

Why do US MPG and UK/Imperial MPG figures differ?

The US liquid gallon is smaller than the Imperial/UK gallon. One Imperial gallon equals exactly 1.20095 US gallons (approximately 4.546 liters vs 3.785 liters). Consequently, a car driving in the UK will appear to have a 20% higher MPG rating because it uses a larger gallon.

Why does the metric system use L/100km instead of km/L?

L/100km measures "fuel consumption" (input divided by output), whereas km/L measures "fuel economy" (output divided by input). L/100km is mathematically linear; lowering consumption from 12L to 10L/100km saves the exact same amount of fuel as lowering from 8L to 6L/100km, which makes comparing car options far more intuitive.

How do you convert km/L directly to US MPG?

Multiply the km/L value by 2.35215 to get the equivalent US MPG rating (e.g., 15 km/L × 2.35215 = 35.28 US MPG).