Fuel Economy Converter

Fuel Economy Converter

Convert between miles per gallon (US), miles per gallon (UK), liters per 100 kilometers, and kilometers per liter. Whether you are comparing vehicles from different countries, reading international car reviews, calculating fuel costs for a road trip, or interpreting manufacturer specs from a foreign market, this converter translates all major fuel efficiency rating systems instantly.

How Fuel Economy Conversion Works

Fuel economy conversions are not simple multiplications because MPG and L/100km measure the same property in opposite directions:

• MPG (US and UK): distance per unit of fuel — higher is more efficient
• L/100km: fuel per unit of distance — lower is more efficient
• km/L: distance per liter — higher is more efficient (Japan’s primary rating)

The core conversion formula is:

• L/100km = 235.215 / US MPG

The constant 235.215 = (1.60934 km/mile) x (3.78541 L/US gallon) x 100

For UK MPG (Imperial gallon = 4.54609 L): L/100km = 282.481 / UK MPG

To convert km/L: km/L = 100 / L/100km, or equivalently km/L = US MPG x 0.42514

Worked Examples

Example 1 — Comparing a US and European car review. A US review rates the Toyota RAV4 Hybrid at 38 US MPG combined. A European review of the same vehicle states 6.2 L/100km. Converting the US rating: 235.215 / 38 = 6.19 L/100km. The figures agree — the small difference is rounding in the test cycle.

Example 2 — Planning a fuel budget for a European road trip. You will drive 1,200 km in a rental car rated at 7.5 L/100km. Fuel needed: (1,200 / 100) x 7.5 = 90 liters. At €1.65/liter, total fuel cost is 90 x 1.65 = €148.50. Converting the car’s rating for context: 235.215 / (100/7.5 x 0.42514) — or simply 235.215 / 31.35 = 7.50 L/100km. Consistent.

Example 3 — Interpreting a Japanese car spec. A Japanese domestic market car is rated at 18 km/L under the WLTC cycle. Converting to US MPG: 18 / 0.42514 = 42.3 US MPG. Converting to L/100km: 100 / 18 = 5.56 L/100km. This is a fuel-efficient compact — roughly equivalent to a 2024 Toyota Corolla Hybrid.

Fuel Economy Reference Table

When to Use This Converter

• You are reading a car review from another country and need to interpret the fuel economy rating in your local units
• You are buying or renting a vehicle abroad and want to estimate fuel costs before the trip
• You want to compare EPA-rated MPG figures against WLTP-rated L/100km figures for the same vehicle sold in two markets
• You are trying to understand whether a UK MPG figure and a US MPG figure describe the same level of efficiency
• You are building a fuel cost spreadsheet and need all vehicles expressed in the same unit (L/100km or US MPG)

Common Mistakes

1. Treating UK MPG and US MPG as equivalent. The UK Imperial gallon is 4.546 L, roughly 20% larger than the US gallon (3.785 L). A car rated at 40 UK MPG is not the same as 40 US MPG — in US terms it is only about 33.3 MPG. Always check which gallon a spec uses before comparing figures.
2. Expecting linear fuel savings from linear MPG gains. Because MPG is in the denominator of the fuel-used formula, gains at low MPG values save far more fuel. Going from 15 to 20 MPG saves 1.67 gallons per 100 miles. Going from 40 to 50 MPG saves only 0.50 gallons per 100 miles. L/100km avoids this distortion — a 1 L/100km improvement always represents the same absolute fuel saving.
3. Comparing EPA, WLTP, and NEDC figures directly. Test cycle results differ: WLTP (Europe since 2017) is generally 10-20% lower than the older NEDC cycle for the same car. EPA figures are roughly similar to WLTP on combined cycles. Always note which test standard was used before comparing efficiency across markets.
4. Confusing km/L with L/100km. Both are metric but they invert each other. A car doing 15 km/L consumes 100/15 = 6.67 L/100km — not 15 L/100km. Japan uses km/L; most of Europe uses L/100km.

Quick Reference Benchmarks

• Average new car sold in the US (2023): about 26 US MPG (9.05 L/100km)
• Average EU passenger car (2022): about 6.1 L/100km (38.6 US MPG)
• Toyota Prius (2024): 57 city / 56 highway US MPG (4.1/4.2 L/100km)
• Full-size pickup truck (2024): 16-20 US MPG (11.8-14.7 L/100km)
• Diesel long-haul truck: approximately 6-8 US MPG (29-39 L/100km)
• Tesla Model 3 Standard Range: 132 MPGe (1.78 L/100km equivalent energy)

Tips

1. When comparing vehicles across markets, convert everything to L/100km — it makes proportional differences in fuel use immediately visible
2. To convert US MPG to L/100km mentally, divide 235 by the MPG figure: 235 / 30 = 7.83 L/100km (accurate to within 0.1%)
3. UK MPG values always look about 20% more impressive than US MPG for the same car — never compare them directly without converting
4. Fuel economy drops significantly at highway speeds above 55-60 mph (88-97 km/h) because aerodynamic drag increases with the square of speed
5. For road trip fuel cost calculations in metric countries: multiply (km driven / 100) by L/100km to get liters needed, then multiply by the price per liter
6. Real-world fuel economy is typically 10-20% lower than official ratings due to air conditioning use, cold weather, cargo load, and individual driving style