🔄 Converters

⛽ ⛽ Fuel Economy Converter: MPG, L/100km, and km/L

Learn how to convert fuel economy between MPG, L/100km, and km/L. Covers the inverse relationship, US vs UK MPG, calculating fuel costs, and electric vehicle efficiency equivalents.

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Fuel economy is measured differently around the world: the US uses miles per gallon (MPG), most other countries use liters per 100 kilometers (L/100km), and some use kilometers per liter (km/L). Critically, MPG and L/100km have an inverse relationship — a higher MPG is better, but a lower L/100km is better. This inverse relationship means you can't simply multiply or divide; you need the correct conversion formula.

The Key Formulas

MPG (US) → L/100km: L/100km = 235.21 ÷ MPG

L/100km → MPG (US): MPG = 235.21 ÷ L/100km

MPG (US) → km/L: km/L = MPG × 0.4251

km/L → MPG (US): MPG = km/L × 2.3521

The constant 235.21 comes from: (100 km × 3.78541 L/gallon) ÷ 1.60934 km/mile.

Conversion Examples

MPG (US)	L/100km	km/L	Context
20	11.76	8.50	Large SUV / truck
30	7.84	12.75	Average sedan
40	5.88	17.0	Efficient hybrid
50	4.70	21.3	Toyota Prius class

US MPG vs UK MPG: A Critical Difference

The US and UK both use "MPG" but with different gallon sizes:

US gallon: 3.785 liters
UK (Imperial) gallon: 4.546 liters

A UK car rated at 40 MPG (Imperial) is only about 33.3 US MPG — a 20% difference. When comparing fuel economy figures, always confirm which MPG is being used.

US MPG → UK MPG: multiply by 1.20095

UK MPG → US MPG: multiply by 0.83267

Calculating Fuel Cost for a Trip

Fuel cost = (Distance ÷ Fuel economy) × Fuel price

Example: 500 km trip, car does 8 L/100km, fuel costs $1.70/L:

Fuel used = 500 ÷ 100 × 8 = 40 liters
Cost = 40 × $1.70 = $68.00

Same trip in MPG: 500 km ≈ 311 miles, car does 29.4 MPG, fuel $6.43/gallon:

Fuel used = 311 ÷ 29.4 = 10.58 gallons | Cost = 10.58 × $6.43 = $68.03 ✓

Electric Vehicle Efficiency: MPGe

Electric vehicles use MPGe (miles per gallon equivalent). The EPA defined 1 gallon of gasoline = 33.7 kWh of energy. So MPGe tells you how far the EV travels on 33.7 kWh.

Tesla Model 3: ~140 MPGe (equivalent to 1.68 L/100km in energy terms)
Nissan Leaf: ~111 MPGe

To calculate EV cost per mile: (electricity cost per kWh × kWh/mile). For a car using 0.3 kWh/mile at $0.13/kWh: 0.3 × $0.13 = $0.039 per mile — roughly 3–4× cheaper than gasoline at most current prices.

Try It Yourself! ✨

Use our free Fuel Economy Converter — results appear as you type. No sign-up needed!

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❓ Frequently Asked Questions

How do I convert MPG to L/100km?▼

L/100km = 235.21 ÷ MPG. Examples: 30 MPG = 235.21÷30 = 7.84 L/100km; 40 MPG = 5.88 L/100km; 25 MPG = 9.41 L/100km. The inverse formula works both ways: MPG = 235.21 ÷ L/100km.

Is higher MPG or lower L/100km better?▼

Both mean better fuel economy — they are inversely related. Higher MPG = better; lower L/100km = better. A 50 MPG car uses only 4.7 L/100km. A 20 MPG car uses 11.8 L/100km. They tell you the same thing from different directions.

What is the difference between US MPG and UK MPG?▼

US and UK gallons are different sizes: US gallon = 3.785 liters, UK imperial gallon = 4.546 liters. A UK car at 40 MPG (Imperial) = about 33.3 US MPG. Multiply UK MPG by 0.833 to get US MPG, or multiply US MPG by 1.201 for UK MPG. When comparing international fuel economy figures, always check which gallon is used.

How do I calculate fuel cost for a road trip?▼

Fuel cost = (Distance ÷ Fuel economy) × Fuel price. In metric: (km ÷ 100) × L/100km = liters needed; liters × price/liter = total cost. Example: 400 km at 7 L/100km = 28 liters; at $1.60/L = $44.80. In US units: miles ÷ MPG = gallons needed; gallons × price/gallon = total cost.

What is MPGe for electric vehicles?▼

MPGe (miles per gallon equivalent) compares EV efficiency to gasoline. The EPA defined 1 gallon of gasoline = 33.7 kWh. MPGe tells you how far the EV travels per 33.7 kWh. A 140 MPGe Tesla uses far less energy per mile than a 30 MPG gasoline car. EV running costs are typically 3–4× lower per mile than gasoline at current energy prices.