⛽ Fuel Economy Converter
Convert between miles per gallon (MPG), liters per 100km and kilometers per liter.
Buying a car from another country? Planning a road trip across borders? Comparing fuel efficiency specs between US and European vehicles can be surprisingly confusing. Our Fuel Economy Converter makes it easy to switch between miles per gallon (MPG), liters per 100 kilometers (L/100km), and kilometers per liter (km/L).
Let’s say you’re shopping for a European hatchback that lists fuel consumption as 5.5 L/100km, but you’re used to thinking in MPG. Enter 5.5 in the value field, select L/100km as “From” and MPG as “To” — the result shows 5.5 L/100km = 42.77 MPG. Now you can meaningfully compare that car’s efficiency against the US-market vehicles you’re already familiar with.
This converter is essential for several real-world situations. Car buyers use it to compare fuel economy across different measurement systems when considering imports. Road trippers converting between the US and Canada or Europe find it invaluable for fuel budgeting — knowing how many liters you’ll need for a 500 km drive given your car’s MPG rating. Fleet managers use it to normalize fuel cost calculations across vehicles with different efficiency standards.
The conversion factors are based on the standard formula: 1 MPG = 235.214 L/100km (or equivalently 1 L/100km = 235.214 / MPG). The converter handles all the math internally, giving you clean, rounded results to 2 decimal places — all the precision you need for trip planning, car comparisons, or fuel budget estimates.
How the conversion works
All three units measure the same physical quantity — fuel consumption — but in different directions. L/100km and km/L are direct reciprocals of each other: a lower L/100km and a higher km/L both mean better efficiency. MPG is yet another way of expressing the same idea.
The tool converts everything through L/100km as its base unit, using two key formulas:
- MPG → L/100km: divide the constant 235.214 by the MPG value. So 30 MPG = 235.214 ÷ 30 = 7.84 L/100km.
- km/L ↔ L/100km: divide 100 by the value. So 10 L/100km = 100 ÷ 10 = 10 km/L, and 15 km/L = 100 ÷ 15 = 6.67 L/100km.
The constant 235.214 comes from the physical relationship between miles, gallons, and liters: 1 US gallon = 3.785 liters and 1 mile = 1.609 km. Combining these gives the conversion factor used worldwide.
Worked example: A car rated at 5.5 L/100km — how efficient is that in MPG? 235.214 ÷ 5.5 = 42.77 MPG. That’s a very economical car by any standard.
Worked example: A US truck rated 18 MPG — what does that mean in km/L? First convert to L/100km: 235.214 ÷ 18 = 13.07 L/100km, then km/L = 100 ÷ 13.07 = 7.65 km/L.
Practical examples with real data
The figures below are computed by hand using the exact formula built into the tool (constant 235.214). All values round to two decimal places, matching the tool’s output.
| From | Value | To | Result |
|---|---|---|---|
| L/100km | 5.5 | MPG | 42.77 MPG |
| MPG | 30 | L/100km | 7.84 L/100km |
| MPG | 18 | km/L | 7.65 km/L |
| L/100km | 10 | km/L | 10.00 km/L |
| km/L | 15 | MPG | 35.28 MPG |
| MPG | 25 | L/100km | 9.41 L/100km |
To verify the last row: 235.214 ÷ 25 = 9.41 L/100km, which matches the tool’s default display exactly. And 15 km/L → MPG goes 100 ÷ 15 = 6.67 L/100km, then 235.214 ÷ 6.67 = 35.28 MPG.
Edge cases and rounding
- Zero is not allowed. Converting a value of 0 would require dividing by zero (235.214 ÷ 0), which is undefined. The tool detects this and asks you to enter a value greater than 0.
- Very low MPG. An inefficient vehicle at 8 MPG converts to 235.214 ÷ 8 = 29.4 L/100km. Extremely high L/100km values are still handled, though they reflect very poor economy.
- Very high MPG / low consumption. A hybrid rated at 50 MPG converts to 235.214 ÷ 50 = 4.70 L/100km. Values stay accurate at two decimals across the normal range.
- US MPG vs. UK MPG. This tool uses US MPG (US gallon of 3.785 L). UK MPG uses the Imperial gallon (4.546 L), so UK figures run about 20% higher. To convert US to UK MPG, multiply by 1.201.
- Decimal inputs. You can enter values like 6.2 L/100km or 42.5 MPG; the tool handles fractional inputs cleanly.
Frequently Asked Questions
Frequently Asked Questions
What's the difference between US MPG and UK MPG?
This converter uses US MPG (based on the US gallon of 3.785 liters). UK MPG uses the Imperial gallon of 4.546 liters, so UK MPG figures are about 20% higher even for the same vehicle. If you need UK MPG, you can convert US MPG by multiplying by 1.201.
When would I use km/L vs L/100km?
km/L is the inverse of L/100km — it tells you how many kilometers you can drive per liter of fuel. It's used in parts of Asia, Africa, and Latin America. L/100km is standard in Europe, Canada, and Australia and indicates how many liters are needed to travel 100 km. The higher the km/L, the better; the lower the L/100km, the better.
Why can't I enter 0 into the converter?
Fuel economy conversion involves division (e.g., 235.214 / MPG), so a value of 0 would result in an undefined calculation. Because of this, the tool displays a helpful message asking you to enter a value greater than 0.
How accurate is the conversion factor 235.214?
The factor 235.214 is the standard conversion constant between US MPG and L/100km, derived from 1 US gallon = 3.785411784 liters and 1 mile = 1.609344 km. It's accurate to three decimal places, which is more than sufficient for fuel economy comparisons and trip planning.
How do I estimate fuel cost for a trip with this converter?
Convert your car's L/100km rating, then multiply by the trip distance divided by 100, then by the fuel price. For example, at 7 L/100km over 500 km you use 7 × 5 = 35 liters. Multiply by your local fuel price per liter to get the total cost. The converter gives you the efficiency figure; the rest is simple multiplication.
Which unit should I use to compare two cars?
Use a single unit for both cars so the comparison is apples-to-apples. L/100km is best for European-market comparisons, while MPG suits US-market comparisons. Convert both cars to the same unit with this tool before judging which is more efficient.
Does this account for city vs. highway driving?
No — the converter only changes units of a number you provide. Real fuel economy varies between city and highway driving, so use the figure that matches your driving pattern (or a combined figure) when converting. The unit conversion itself is always correct regardless.
Is a higher MPG always better?
Yes — higher MPG means more miles per gallon, so better fuel economy. The same logic applies to km/L. L/100km is the opposite: a lower number means better economy. The converter preserves this relationship correctly whichever unit you use.
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This converter is maintained by Aren Breur, the editor of ConvertAny.app. Aren builds fast, free browser-based tools that make everyday conversions simple without sign-ups or data collection. If you have feedback or a converter you would like added, reach out via the contact page or email aren2connect@gmail.com.