Fuel Efficiency Converter
This fuel efficiency converter accepts miles per gallon (MPG) and converts it to liters per 100 km and km per liter, covering the three main fuel economy standards used worldwide. It is indispensable when comparing vehicles across different markets.
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Formula
L/100km = 235.214 ÷ MPG
The factor 235.214 comes from converting the units: 1 US gallon = 3.78541 liters, and 1 mile = 1.60934 km. Since L/100km is an inverse efficiency (lower is better), the formula is a reciprocal relationship: L/100km = (100 × 3.78541) ÷ (MPG × 1.60934) = 235.214 ÷ MPG.
How to use the Fuel Efficiency Converter
- 1
Enter your fuel economy (mpg)
Enter fuel economy in miles per gallon (US MPG) to convert to other units.
- 2
Read your results instantly
Results update in real time as you type.
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Three Fuel Economy Standards
Fuel efficiency is reported differently around the world, creating confusion when comparing vehicles or planning fuel budgets across borders. The US, UK (traditionally), and some other countries use miles per gallon (MPG), where higher numbers are better. Most of Europe, Asia, and South America use liters per 100 km (L/100km), where lower numbers are better — an important inversion to note. Japan and some other Asian markets use km per liter (km/L), analogous to MPG but in metric. This converter handles all three, making international vehicle comparisons straightforward.
Why L/100km and MPG Are Inversely Related
Miles per gallon and liters per 100 km are inversely related: as MPG goes up, L/100km goes down. This means a 1 MPG improvement at high efficiency (e.g., from 40 to 41 MPG) saves less fuel than a 1 MPG improvement at low efficiency (e.g., from 15 to 16 MPG). In L/100km terms, the fuel savings are more intuitive — each liter reduction per 100 km is a consistent saving. This is why fuel economy standards in Europe use L/100km rather than the equivalent of MPG. When evaluating vehicles, compare them in the same unit to avoid misleading conclusions from the inverse relationship.
Tips & Insights
Higher MPG Does Not Mean Equal Savings
Due to the inverse relationship, improving a car from 15 to 20 MPG saves more fuel than improving from 40 to 50 MPG. This is clearer in L/100km: 15 MPG = 15.7 L/100km, 20 MPG = 11.8 L/100km (saving 3.9 L), while 40→50 MPG saves only 1.2 L/100km.
US vs. UK MPG
The US gallon (3.785 L) is smaller than the UK imperial gallon (4.546 L). A car rated at 30 US MPG equals about 36 UK MPG. Always confirm whether an MPG figure uses US or UK gallons when comparing international vehicle specs.
Electric Vehicle Equivalent
Electric vehicles use MPGe (miles per gallon equivalent), where 33.7 kWh of electricity is treated as equivalent to one gallon of gasoline. This allows apples-to-apples comparison of EV and ICE vehicle efficiency on window stickers.
Worked Examples
Average US Car (27 MPG)
27 MPG equals 8.71 L/100km, 11.48 km/L, and 7.13 miles/liter — typical US sedan fuel economy.
Fuel-Efficient Hybrid (55 MPG)
55 MPG equals 4.28 L/100km, 23.38 km/L, and 14.52 miles/liter — typical Toyota Prius highway economy.
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Frequently Asked Questions
How do you convert MPG to L/100km?
Divide 235.214 by the MPG value to get liters per 100 km. For example, 30 MPG = 235.214 ÷ 30 = 7.84 L/100km. The factor 235.214 comes from combining the liter-to-gallon and mile-to-km conversion factors.
Is 8 L/100km good fuel efficiency?
8 L/100km is about average for a modern passenger car. Fuel-efficient small cars achieve 5–6 L/100km; SUVs and trucks average 9–14 L/100km. In MPG, 8 L/100km equals about 29.4 MPG.
What is the difference between US MPG and UK MPG?
The US gallon is 3.785 liters while the UK imperial gallon is 4.546 liters. A car rated at 30 US MPG is equivalent to approximately 36 UK MPG. This 20% difference can cause significant confusion when comparing vehicle specs from different markets.
How much does fuel efficiency affect annual fuel costs?
Fuel cost savings depend on how much you drive. At 15,000 miles/year and $3.50/gallon, the difference between 25 and 30 MPG saves about $350 per year. Use a fuel cost calculator to estimate your specific savings.
What is MPGe for electric vehicles?
MPGe (miles per gallon equivalent) is a metric used by the US EPA to compare EV efficiency with traditional vehicles. 33.7 kWh of electrical energy is defined as equivalent to 1 gallon of gasoline. A car achieving 100 MPGe uses 33.7 kWh to travel 100 miles.
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