Fuel Efficiency Converter
Convert between km/L, miles per gallon (US & UK), and L/100km for comparing fuel economy across standards.
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.
The four conventions and how they differ
- Miles per US gallon (MPG) — used in the US. Higher is better. 30 MPG is mediocre, 40+ MPG is efficient.
- Miles per UK (Imperial) gallon — used in the UK. Imperial gallon is 4.546 L; US gallon is 3.785 L. A car rated "40 MPG UK" is roughly "33 MPG US" — same fuel use, different gallon. Confusion is constant when comparing UK and US car reviews.
- Litres per 100 km (L/100 km) — used in most of Europe and Australia. Lower is better. 5 L/100 km is efficient; 12 L/100 km is thirsty.
- Kilometres per litre (km/L) — used in India, Japan, and parts of Latin America. Higher is better.
Conversion formulas
| From | To | Formula |
|---|---|---|
| MPG (US) | L/100 km | 235.215 ÷ MPG |
| L/100 km | MPG (US) | 235.215 ÷ L/100km |
| MPG (UK) | L/100 km | 282.481 ÷ MPG |
| MPG (US) | MPG (UK) | MPG × 1.20095 |
| km/L | L/100 km | 100 ÷ km/L |
| km/L | MPG (US) | km/L × 2.35215 |
Why L/100 km behaves better mathematically
MPG is non-linear in fuel saved. Going from 15 to 30 MPG saves enormously more fuel per mile than going from 30 to 60 MPG, even though both look like "doubling efficiency". L/100 km is linear in fuel: going from 16 to 8 L/100 km is exactly the same fuel reduction per kilometre whether you call it "halving consumption" or any other framing. This is why EU fuel-economy regulations and most engineering analyses use L/100 km rather than MPG.
Worked example: comparing two used cars
Car A: 28 MPG (US). Car B: 7 L/100 km. Which uses less fuel? Convert A: 235.215 ÷ 28 = 8.4 L/100 km. So B (at 7) uses about 17% less fuel per kilometre than A. Over 15,000 km/year and €1.80/L petrol, that is roughly €380/year of fuel savings — meaningful but not transformative.
Electric vehicles
- MPGe (miles per gallon equivalent) — US EPA convention. 1 gallon of gasoline = 33.7 kWh. Tesla Model 3 RWD is rated ~132 MPGe.
- kWh/100 km — European convention. Most efficient EVs are 14–16 kWh/100 km city, 18–22 highway.
- Wh/mile or Wh/km — what most EV dashboards display. 250 Wh/mile ≈ 156 Wh/km ≈ 15.6 kWh/100 km.
Frequently Asked Questions
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.