Fuel Efficiency Converter

Convert between km/L, miles per gallon (US & UK), and L/100km for comparing fuel economy across standards.

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Quick Reference

Understanding Fuel Efficiency Units

Different countries measure fuel efficiency differently. The US uses miles per gallon (MPG), most of Europe and Asia use litres per 100 km (L/100km), and some countries like India and Japan use km/L. Understanding these units is essential when comparing vehicles across markets.

Key Formulas

km/L → L/100km: L/100km = 100 ÷ km/L
km/L → MPG (US): MPG = km/L — 2.35215
km/L → MPG (UK): MPG = km/L — 2.82481
MPG (US) ? km/L: km/L = MPG — 2.35215

Common Equivalents

km/L	MPG (US)	MPG (UK)	L/100km
5	11.76	14.12	20.00
10	23.52	28.25	10.00
15	35.28	42.37	6.67
20	47.04	56.50	5.00
25	58.80	70.62	4.00

Note on L/100km

L/100km is an inverse unit — a lower number means better efficiency. A car getting 5 L/100km is more efficient than one getting 10 L/100km. This is opposite to km/L and MPG where higher is better.

Frequently Asked Questions

A UK (imperial) gallon is about 20% larger than a US gallon (4.546 L vs 3.785 L). So you travel more miles on one imperial gallon, making the UK MPG number higher for the same car.

For petrol cars, 15—20 km/L (35—47 MPG US) is considered good. Hybrids can achieve 20—30 km/L (47—70 MPG US). Diesel cars typically get 18—25 km/L. Electric vehicles are measured in kWh/100km instead.

Simply divide 100 by the L/100km value. For example, 8 L/100km = 100 ÷ 8 = 12.5 km/L. They have an inverse relationship.

Fuel-efficiency systems are not interchangeable by simple multiplication

Three popular ways of measuring how much fuel a vehicle uses behave differently because two of them measure distance per fuel and one measures fuel per distance. Higher MPG (miles per gallon) is better; higher km/L (kilometres per litre) is better; but lower L/100km (litres per hundred kilometres) is better. They are reciprocal, so comparing them directly invites confusion.

Conversion anchors

MPG (US) to L/100km: 235.215 / MPG
MPG (UK) to L/100km: 282.481 / MPG
L/100km to km/L: 100 / L/100km
1 US gallon = 3.7854 L; 1 UK gallon = 4.5461 L

Why US and UK MPG differ by 20 percent

Because their gallons are different sizes. A US gallon is about 3.79 litres; an imperial gallon (still used in some UK contexts) is about 4.55 litres. A car that does 30 MPG in the US would do about 36 MPG by imperial measurement — same car, same consumption, different unit.

Practical applications

Trip-cost estimates depend on fuel price per litre or per gallon, distance, and the vehicle's real-world efficiency (typically 80–90% of the manufacturer's rated figure). For mixed driving, take the rated combined number and shave 10% to plan conservatively. For motorway-only driving, use the highway figure as is.