Fuel Economy Converter — MPG, L/100km & km/L Explained
By sadiqbd · June 5, 2026
Fuel economy numbers mean nothing until you convert them
A car review from the US says "32 miles per gallon." A European spec sheet quotes "7.2 litres per 100 km." An Indian listing shows "16 km/l." These are three different ways of expressing fuel efficiency — and without converting, comparing them is impossible.
Fuel economy is also one of those measurements where unit choice genuinely affects intuition. MPG makes high numbers look good (bigger = better). L/100km inverts this — smaller is more efficient. Switching between them, or between metric and imperial systems, requires a conversion that's just annoying enough to trip people up. A fuel economy converter does it instantly.
The Main Fuel Economy Units
Miles per gallon (MPG)
The standard in the US and UK (though the UK gallon is larger than the US gallon — an important distinction). Higher = more efficient.
- US MPG: based on the US liquid gallon (3.785 litres)
- UK MPG (Imperial MPG): based on the Imperial gallon (4.546 litres) — about 20% higher than US MPG for the same efficiency
Litres per 100 kilometres (L/100km)
The standard in most of Europe, Australia, and increasingly elsewhere. Lower = more efficient. The inversion relative to MPG is what makes direct comparison confusing — a car with better fuel economy has a lower L/100km but a higher MPG.
Kilometres per litre (km/L)
Common in South Asia, Japan, and parts of Latin America. Higher = more efficient. More intuitive for people used to thinking "how far does a tank take me."
Miles per litre (mi/L)
Less common; occasionally seen in older UK publications or comparisons.
Key Conversions
| From | To | Multiply by |
|---|---|---|
| km/L | L/100km | 100 ÷ km/L value |
| L/100km | km/L | 100 ÷ L/100km value |
| US MPG | L/100km | 235.21 ÷ MPG value |
| L/100km | US MPG | 235.21 ÷ L/100km value |
| km/L | US MPG | multiply by 2.352 |
| UK MPG | US MPG | multiply by 0.8327 |
The MPG ↔ L/100km relationship is inverse — you divide a constant by the value, which is why doubling MPG doesn't halve L/100km linearly.
How to Use the Fuel Economy Converter on sadiqbd.com
- Enter the fuel economy value — the figure from a spec sheet or review.
- Select the source unit — MPG (US), MPG (UK/Imperial), L/100km, or km/L.
- Select the target unit — the unit you want to compare in.
- Read the result — instant conversion.
Real-World Examples
Comparing cars across markets
You're comparing three cars:
- Car A (US spec): 34 MPG (US)
- Car B (European spec): 5.8 L/100km
- Car C (Bangladesh/India spec): 18 km/L
Converting all to km/L:
- Car A: 34 US MPG × 0.4251 = 14.45 km/L
- Car B: 100 ÷ 5.8 = 17.24 km/L
- Car C: 18 km/L
Car C is most efficient, followed by Car B, then Car A — something you couldn't see at all without converting.
Calculating fuel cost for a trip
Your car does 14 km/L. You're planning a 450 km trip. Petrol costs ৳125/litre.
Fuel needed: 450 ÷ 14 = 32.14 litres Fuel cost: 32.14 × 125 = ৳4,018
If you're comparing against a car doing 18 km/L: Fuel needed: 450 ÷ 18 = 25 litres Fuel cost: 25 × 125 = ৳3,125
The more efficient car saves ৳893 on this trip — and the gap compounds over thousands of kilometres annually.
Understanding a European spec
A German car is rated at 4.9 L/100km combined. Converting to MPG (US) for comparison with American cars:
4.9 L/100km → 235.21 ÷ 4.9 = 48 US MPG
That's well above the average American car. In Bangladesh km/L terms: 100 ÷ 4.9 = 20.4 km/L — an efficient car by any measure.
Real-world vs. rated efficiency
Car manufacturers quote test-cycle efficiency, which real-world driving typically doesn't match. A car rated at 16 km/L in city driving might realistically achieve 13–14 km/L in Dhaka traffic.
13 km/L → 235.21 ÷ (100/13) = 235.21 ÷ 7.69 = 30.6 US MPG 14 km/L → 32.9 US MPG
Tracking your actual fuel economy (fill up, reset odometer, fill up again and divide km driven by litres added) gives you the real number to work with.
Why the US and UK MPG Figures Differ
The US gallon (3.785 L) and the UK Imperial gallon (4.546 L) are different units. A car doing 40 UK MPG gets:
40 UK MPG × (4.546 L/gallon ÷ 3.785 L/gallon) = 40 × 1.201 = 48 US MPG
This is why British car reviews can quote MPG figures that seem dramatically better than American reviews of the same car — they're measuring with a bigger "gallon." Always check which MPG standard is being used. A "40 MPG" claim from a US source and a British source represent meaningfully different efficiencies.
Tips for Comparing Fuel Economy
Use L/100km for objective comparison. Unlike MPG, L/100km is directly proportional to fuel cost — twice the L/100km means twice the fuel bill. MPG is inversely proportional, which makes comparisons less intuitive.
Calculate annual fuel cost, not just efficiency rating. A car doing 12 km/L vs. one doing 15 km/L — how much does the difference actually cost over a year? If you drive 20,000 km/year at ৳125/litre: 20,000/12 × 125 = ৳2,08,333 vs. 20,000/15 × 125 = ৳1,66,667. That's ৳41,666 per year — meaningful.
Track your own fuel economy. Manufacturer ratings are test-cycle figures. Your actual fuel economy depends on driving style, traffic, AC use, tyre pressure, and load. Tracking it over a few fill-ups gives a much more useful number.
City vs. highway efficiency varies significantly. Most cars are 20–40% more efficient on highways than in city driving. If your usage is mostly city, weight the city figure more heavily when comparing cars.
Frequently Asked Questions
Is UK MPG the same as US MPG? No — the UK uses the Imperial gallon (4.546 L), while the US uses the US liquid gallon (3.785 L). UK MPG figures are about 20% higher than US MPG for the same fuel efficiency. Always check which standard a review uses.
Which is better: higher MPG or lower L/100km? Both mean more efficient. Higher MPG = better. Lower L/100km = better. They're inversely related to each other.
How do I calculate fuel economy from a fill-up? Reset your trip odometer when you fill up. Next time you fill up, note the km driven and litres added. km ÷ litres = km/L. This is your actual real-world efficiency.
What's a good fuel economy for a city car in Bangladesh? In Dhaka city traffic, a modern compact petrol car typically achieves 10–14 km/L. Hybrid cars can achieve 18–22 km/L in city conditions. CNG vehicles vary but often achieve equivalent economics at lower running cost.
Is the fuel economy converter free? Yes — completely free, no sign-up needed.
Fuel economy figures are useless if you can't compare them across systems. Whether you're evaluating a car purchase, planning a road trip budget, or just trying to understand what a European spec sheet is telling you, the converter puts everything on the same footing instantly.
Try the Fuel Economy Converter free at sadiqbd.com — convert MPG, L/100km, and km/L instantly.
