Fuel Efficiency Converter
Energy & PowerConvert fuel efficiency between km/L, L/100km, and mpg instantly. Supports US and UK gallons — ideal for comparing Indian and international car mileage.
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What is a Fuel Efficiency?
A Fuel Efficiency Converter translates a vehicle's mileage or fuel consumption figure between the major unit systems used around the world — kilometres per litre (km/L), litres per 100 kilometres (L/100km), miles per gallon in US measure (mpg US), miles per gallon in UK imperial measure (mpg UK), and miles per litre (mi/L).
Fuel efficiency is not a single universal scale. India and Japan express it as distance per unit volume (km/L — higher is better). Continental Europe and Australia express it as volume per unit distance (L/100km — lower is better). The United States and the United Kingdom both use miles per gallon, but their gallons are different volumes: a US gallon is 3.7854 litres, while a UK imperial gallon is 4.5461 litres — making US and UK mpg figures incompatible without conversion.
This divergence creates real confusion for Indian car buyers. A European car review says a model returns 5.5 L/100km; an American review says 43 mpg; the Indian brochure says 18.2 km/L. These are all the same car, and with this converter, you can verify that immediately.
The Fuel Efficiency Converter is also useful for evaluating imported vehicles, comparing international driving data from navigation apps, understanding fuel economy standards (like the US EPA or EU WLTP cycle ratings), and cross-checking taxi or fleet operator benchmarks from different regions.
Conversions in this tool are non-linear — you cannot convert between km/L and L/100km with a fixed multiplier because the two scales are reciprocals. The converter applies mathematically exact formulas for every unit pair. For additional context on how distance and speed relate to fuel consumption, see the Speed Converter.
How to use this Fuel Efficiency calculator
- Locate the FROM dropdown and select the unit your mileage figure is in — for example,
Kilometres per Litre (km/L). - Enter your numeric value in the input field, such as
18for a car rated at 18 km/L. - Select the target unit in the TO dropdown — for example,
Miles per Gallon — US (mpg)to see how it compares with an American car review. - The converted result appears instantly in the output panel — no button press needed.
- Use the ⇅ swap button between the panels to reverse the conversion (e.g. convert from mpg back to km/L).
- Scroll to the reference table to see your entered value expressed in all five units at the same time — useful for a full cross-regional picture.
- Copy the URL from your browser to share this exact conversion with a colleague or save it for later.
Formula & Methodology
This converter uses km/L as its canonical intermediate unit. Every other unit converts to km/L first, then from km/L to the target. Exact conversion constants used: | Constant | Value | Source | |---|---|---| | 1 mile | 1.609344 km | International yard and pound agreement, exact | | 1 US gallon | 3.785411784 L | US customary definition, exact | | 1 UK gallon | 4.54609 L | UK Weights and Measures Act, exact | Formulas (via km/L as intermediate): | From | To km/L | From km/L | |---|---|---| | L/100km |100 ÷ value|100 ÷ km_l| | mpg (US) |value × 1.609344 ÷ 3.785412|km_l ÷ 1.609344 × 3.785412| | mpg (UK) |value × 1.609344 ÷ 4.54609|km_l ÷ 1.609344 × 4.54609| | mi/L |value × 1.609344|km_l ÷ 1.609344| L/100km ↔ mpg (US) shortcut formula (derived from the above):mpg (US) = 235.214 ÷ L/100km L/100km = 235.214 ÷ mpg (US)Worked example — comparing a European and Indian rating: A Volkswagen Polo is rated at 4.9 L/100km (European WLTP). The Indian brochure claims 19.47 km/L (ARAI).European figure → km/L: 100 ÷ 4.9 = 20.41 km/L Indian ARAI figure: 19.47 km/LThe ARAI figure is slightly lower because ARAI test conditions differ from WLTP. Both are in the same ballpark — confirming the Indian specification is credible. Common reference table: | km/L | L/100km | mpg (US) | mpg (UK) | |---|---|---|---| | 8 | 12.50 | 18.82 | 22.60 | | 10 | 10.00 | 23.52 | 28.25 | | 12 | 8.33 | 28.23 | 33.89 | | 15 | 6.67 | 35.28 | 42.37 | | 18 | 5.56 | 42.34 | 50.85 | | 20 | 5.00 | 47.04 | 56.50 | | 25 | 4.00 | 58.81 | 70.62 |
Frequently Asked Questions
What is a fuel efficiency converter?
A fuel efficiency converter is a tool that translates a vehicle's mileage figure from one unit of measurement to another — such as from kilometres per litre (km/L) to litres per 100 kilometres (L/100km) or miles per gallon (mpg). Because different countries use fundamentally different scales to express the same concept, direct comparison is impossible without conversion. This tool handles all major units — km/L, L/100km, mpg (US), mpg (UK), and miles per litre — in a single step.
What is the difference between km/L and L/100km?
Kilometres per litre (km/L) tells you how far a vehicle travels on one litre of fuel — higher is better. Litres per 100 km (L/100km) tells you how many litres are consumed over 100 km — lower is better. The two are reciprocals: L/100km = 100 ÷ km/L. A car rated at 15 km/L consumes 6.67 L/100km. India and Japan typically use km/L, while Europe and Australia use L/100km.
What is the difference between US mpg and UK mpg?
Both measure miles per gallon, but the US gallon (3.7854 litres) and the UK imperial gallon (4.5461 litres) are different volumes. A car rated at 40 mpg (US) is actually rated at about 48 mpg (UK) — the same physical vehicle, the same fuel consumption, just a different gallon. This is a common source of confusion when comparing American and British car reviews, and why this converter distinguishes between the two.
How do I convert km/L to mpg?
To convert km/L to US mpg, multiply by 2.35215 (or equivalently, multiply by 1.609344 and divide by 3.785412). For example, 15 km/L × 2.35215 = 35.28 mpg (US). To convert to UK mpg, multiply by 2.82481 instead. Using this converter, enter your km/L value in the FROM field, select 'Kilometres per Litre (km/L)', and choose 'Miles per Gallon — US (mpg)' in the TO field.
How do I convert L/100km to mpg?
L/100km to mpg (US) uses the formula: mpg = 235.214 ÷ L/100km. So 7 L/100km = 235.214 ÷ 7 = 33.6 mpg (US). For UK mpg, use 282.481 ÷ L/100km. Note that this is a reciprocal relationship — you cannot simply multiply or divide by a constant, which is why this converter uses a non-linear formula rather than a fixed multiplier.
What is a good mileage figure for a car in India?
For Indian driving conditions — a mix of city stop-and-go and highway — a petrol car returning 15–18 km/L is considered good, and diesel cars often achieve 18–22 km/L. Small hatchbacks like the Maruti Swift and Hyundai Grand i10 typically return 18–20 km/L under test conditions; real-world figures are usually 10–15% lower. SUVs and larger sedans typically fall in the 10–14 km/L range. The ARAI (Automotive Research Association of India) certifies official mileage figures under controlled conditions.
What unit of fuel efficiency does India use?
India officially uses kilometres per litre (km/L), consistent with the metric system and similar to Japan and most Asian markets. The Bureau of Indian Standards and ARAI publish mileage certifications in km/L. Fuel economy labels on new cars sold in India display km/L figures, and fuel price comparisons are always based on cost per litre. Some enthusiast communities also reference L/100km when comparing with European car reviews.
How do I use this Fuel Efficiency Converter?
Enter a numeric value in the input field, then select your source unit from the FROM dropdown — for example, 'Kilometres per Litre (km/L)'. Choose the target unit in the TO dropdown, such as 'Miles per Gallon — US (mpg)'. The converted result appears instantly. Use the ⇅ swap button to reverse the direction, and view the reference table below to see your input expressed in all five units simultaneously.
Why can't fuel efficiency be converted with a simple multiplier?
Kilometres per litre and litres per 100 km express fuel efficiency as inverses of each other. When you double your km/L, you halve your L/100km — not a fixed multiplication. Because L/100km = 100 ÷ km/L, no single constant can convert between them linearly. The mpg units add another layer: they use volume units (US gallon, UK gallon) that differ from the litre. This converter applies the correct reciprocal and volume-conversion formulas for each unit pair.
What is 20 km/L in mpg (US)?
20 km/L equals approximately 47.04 mpg (US). The calculation is: 20 × (1.609344 ÷ 3.785412) = 20 × 0.42514 = 8.503 km per 100 miles... or more directly, 20 × 2.35215 = 47.04 mpg (US). In UK mpg, the same 20 km/L equals approximately 56.5 mpg (UK). This is an excellent figure — roughly equivalent to a modern petrol hybrid in Indian highway conditions.
How does fuel efficiency affect running costs in India?
At a petrol price of ₹100 per litre, a car returning 15 km/L costs ₹6.67 per km, while one returning 20 km/L costs just ₹5 per km. Over 15,000 km per year (a common estimate for Indian drivers), the difference is ₹25,000 annually. For a car loan financed over 5 years, fuel savings can equal or exceed the difference in on-road price between a base and a higher-spec variant — making mileage one of the most financially significant specifications. See the [Car Loan EMI Calculator](/car-loan-emi-calculator/) to factor in financing costs alongside running expenses.
What is miles per litre and when is it used?
Miles per litre (mi/L) is a hybrid unit that combines the imperial distance measure (miles) with the metric volume measure (litres). It is rarely used in official ratings but appears in British fuel economy discussions and is sometimes used in aviation and marine contexts. One mile per litre equals 1.60934 km/L. It is included in this converter for completeness and for users comparing sources that mix unit systems.