Fuel Efficiency Converter (All-in-One)
Convert km/l, L/100km, mpg (US & UK) instantly
Converted Values
km/l: 20.00
L/km: 0.05
L/100km: 5.00
MPG (US): 47.04
MPG (UK): 56.50
Formula
Base unit: km/l
MPG (US) = km/l ÷ 0.425144
L/100km = 100 ÷ km/l
What Is the Fuel Efficiency Converter (All-in-One)?
This fuel efficiency converter takes a single value and instantly shows it in kilometers per liter (km/l), liters per km, liters per 100 km, and miles per gallon in both the US and UK definitions — useful for comparing car, bike, and truck fuel consumption figures across countries that measure it differently.
The differences here aren't just about metric versus imperial units — they also reflect genuinely different national testing and reporting traditions. The United States began requiring fuel economy window stickers and average fleet standards (CAFE — Corporate Average Fuel Economy) in 1975, in direct response to the 1973 oil crisis, and settled on miles per gallon as the public figure. Most of Europe and Asia instead adopted liters per 100 km, which flips the relationship: it measures fuel consumed over a fixed distance rather than distance covered per unit of fuel, so a lower number means better efficiency — the opposite of km/l or mpg. To make things trickier, the US and UK gallon aren't even the same size: the imperial (UK) gallon, at 4.54609 liters, is about 20% larger than the US gallon's 3.78541 liters, so the same physical vehicle produces two different mpg numbers depending on which gallon is used.
This calculator handles all four conventions at once, so you don't have to track which country's standard a figure came from. If your trip planning also involves distances or speeds, the Length Converter and Speed Converter cover those conversions too.
Fuel Efficiency Converter (All-in-One) Formula
- 1 km/l = 2.35215 MPG (US)
- 1 MPG (US) ≈ 0.425 km/l
- L/100km = 100 ÷ km/l
How Is the Fuel Efficiency Converter (All-in-One) Calculated?
km/l and MPG both measure distance per unit of fuel, so they scale directly by a fixed conversion factor. L/100km flips the relationship to measure fuel consumed per fixed distance instead, which is why it moves in the opposite direction — a lower L/100km means better efficiency, unlike km/l or MPG where higher is better.
The US and UK mpg figures differ because they're built on differently sized gallons rather than a different measurement of fuel use: converting km/l to mpg means multiplying by however many miles are in a kilometer and however many gallons are in a liter, and since a US gallon (3.78541 L) is smaller than a UK gallon (4.54609 L), the same vehicle needs more (smaller) US gallons to travel the same distance, which produces a lower US mpg number than UK mpg for identical real-world fuel consumption.
Fuel Efficiency Converter (All-in-One) Example
A car rated at 15 km/l converts to roughly 35.3 MPG (US), or about 6.67 L/100km.
A car consuming 8 L/100km converts to 100 ÷ 8 = 12.5 km/l, or roughly 29.4 MPG (US) and 35.3 MPG (UK).
A US-market truck rated at 40 MPG (US) converts to 40 × 0.425144 ≈ 17.01 km/l, or about 5.88 L/100km.
How to Use the Fuel Efficiency Converter (All-in-One)
Step 1
Enter a fuel efficiency value.
Step 2
Select the unit it currently represents.
Step 3
View the converted efficiency across all supported units instantly.
Step 4
Switch the input unit to compare a manufacturer spec against a unit you're used to.
Step 5
Use the L/100km figure when estimating total fuel cost for a known trip distance.
Step 6
Double-check whether a foreign mpg figure is US or UK before comparing it directly.
Benefits
- Bridges metric (km/l, L/100km) and imperial (MPG) fuel economy standards in one tool.
- Distinguishes US and UK gallons, which are meaningfully different sizes despite the shared name.
- Helps compare vehicle specs sourced from manufacturer listings in different countries.
- Removes the mental step of inverting L/100km to compare it against km/l or mpg.
- Turns a raw fuel-economy figure into a clean, shareable image summary.
- Free to use instantly in the browser, with no spreadsheet or manual formula needed.
Common Fuel Efficiency Converter (All-in-One) Scenarios
Scenario 1
Comparing a car's advertised fuel economy across regions before an international purchase.
Scenario 2
Estimating fuel costs for a road trip using a consistent unit.
Scenario 3
Understanding manufacturer specs listed in an unfamiliar unit on an import vehicle.
Scenario 4
Comparing a rental car's quoted fuel economy abroad to what you're used to at home.
Scenario 5
Working out real-world efficiency from a fill-up (distance driven ÷ fuel used) and converting it for comparison.
Scenario 6
Evaluating motorcycle or scooter fuel efficiency figures given in an unfamiliar unit.
Understanding Your Result
Each figure expresses the same fuel efficiency on a different scale. Remember that km/l and MPG increase with better efficiency, while L/100km decreases with better efficiency — they represent the relationship inversely.
A few reference points make it easier to judge whether a figure is decent:
| km/l | L/100km | MPG (US) | MPG (UK) |
|---|---|---|---|
| 10 | 10.00 | 23.52 | 28.25 |
| 15 | 6.67 | 35.28 | 42.37 |
| 20 | 5.00 | 47.04 | 56.50 |
Tips
- Watch for whether a source uses US or UK gallons — they differ by about 20%.
- Use L/100km when comparing fuel costs directly, since it scales with distance traveled.
- Real-world fuel efficiency often differs from manufacturer specs due to driving conditions.
- When averaging fuel economy across a trip, average the L/100km or km/l figures rather than averaging mpg directly, since mpg doesn't average linearly with distance.
- City and highway ratings can differ substantially — check which one a source is quoting before comparing vehicles.
Common Mistakes
- Mixing up US MPG and UK MPG, which represent different actual fuel economy for the same number.
- Forgetting that L/100km is inverted — a smaller number means better efficiency, unlike the other units.
- Comparing efficiency figures measured under different testing standards without noting the difference.
- Averaging mpg values directly across multiple trips instead of averaging fuel-per-distance figures, which introduces error.
- Assuming a car's official rating will exactly match real-world results, when driving style and conditions typically shift it by 10-20%.
Frequently Asked Questions
Which is better, km/l or mpg?
Both measure the same thing — distance per unit of fuel — but km/l is commonly used in India and Europe, while mpg is standard in the US and UK.
Why is L/100km used?
L/100km shows fuel consumption rather than efficiency — a lower L/100km number means better fuel economy, which some people find more intuitive for comparing costs.
Is UK mpg different from US mpg?
Yes, the UK (imperial) gallon is larger than the US gallon, so the same fuel efficiency produces different mpg values between the two systems.
How much bigger is a UK gallon than a US gallon?
A UK (imperial) gallon is about 20% larger than a US gallon, which is why UK MPG figures are typically higher than US MPG for the same actual fuel efficiency.
Why does my actual fuel economy differ from the sticker rating?
Official ratings are measured under standardized test conditions; real-world factors like driving style, terrain, weather, and vehicle load can meaningfully change actual fuel economy.
What is a good L/100km value?
It depends on the vehicle type, but many modern passenger cars range from about 5-8 L/100km, with hybrids and small cars often below 5.
Why does the same car show different fuel efficiency numbers in different countries?
Different countries use different measurement units (mpg vs. km/l vs. L/100km) and different testing standards or cycles, both of which affect the numbers reported for the same vehicle.
Is a higher or lower L/100km number better?
Lower is better for L/100km, since it represents less fuel consumed per 100 km traveled — this is the opposite direction from mpg or km/l, where higher numbers indicate better efficiency.
Does this calculator account for electric or hybrid vehicle efficiency?
No — this converter is designed for traditional fuel-consumption units (km/l, mpg, L/100km); electric vehicle efficiency is typically measured in different units like miles/kWh or kWh/100km.
Can I share this conversion as an image?
Yes — tap Share and, on supported devices, your conversion is shared as a branded image card, not just a text link.
Why did the US start requiring fuel economy ratings on cars?
The US introduced fuel economy window stickers and Corporate Average Fuel Economy (CAFE) standards in 1975, directly in response to the 1973 oil crisis, aiming to reduce national fuel consumption and give buyers comparable efficiency figures.
How do I estimate my own real-world fuel efficiency from a fill-up?
Divide the distance driven since your last full tank by the amount of fuel added to fill it back up (for example, 450 km driven ÷ 30 liters used = 15 km/l), then enter that figure here to convert it to other units.
Does a higher-priced fuel type change how fuel efficiency is measured?
No — km/l, L/100km, and mpg all measure volume of fuel per distance regardless of fuel grade or price; a more expensive premium fuel doesn't change the unit conversion, only the cost calculation built on top of it.
Why do some manufacturer specs list a range instead of a single fuel efficiency number?
Manufacturers often report separate city and highway (or urban/extra-urban) figures, plus a combined average, because fuel efficiency genuinely differs between stop-and-go and steady-speed driving — check which figure a source is quoting before converting or comparing it.
References
Important Information
All conversions are based on standard unit definitions for US and UK measurements.
Last updated: July 25, 2026