Fuel Efficiency Converter

About Fuel Efficiency Converter

The Fuel Efficiency Converter instantly converts fuel economy between MPG (US gallons), MPG (Imperial gallons), L/100km, km/L and mi/L. Beyond a plain conversion, the tool ranks the result on a colored efficiency gauge, matches it to a vehicle class (EV, hybrid, sedan, SUV, pickup), projects how far one tank will take you, estimates fuel cost, and shows an approximate CO2 footprint per 100 km. It is designed for drivers comparing US and European specs, fleet operators planning trips, and anyone trying to understand whether a number on a brochure is good or thirsty.

Why fuel-economy units are easy to confuse

The same physical fact - "this car uses gasoline at this rate" - is reported in two opposite directions around the world:

• Distance per fuel (higher is better): MPG (US), MPG (Imperial), km/L, mi/L. North America, the UK, India, Japan and Latin America.
• Fuel per distance (lower is better): L/100km. Most of Europe, Australia, China, South Africa.

Mixing the two leads to wrong intuitions. A car rated at 5 L/100km is more efficient than one at 8 L/100km, but the same car rated at 47 MPG (US) is more efficient than one at 30 MPG (US). This converter shows both directions side-by-side so you never have to second-guess.

Reference: typical economy by vehicle class

How to Use the Fuel Efficiency Converter

1. Enter the value shown on your trip computer or vehicle spec sheet.
2. Pick the unit it is currently in (MPG US, MPG Imperial, L/100km, km/L or mi/L).
3. Optional: add tank size in liters and fuel price per liter to see range and cost projections.
4. Read the result. All five units are shown along with an efficiency gauge, vehicle-class match, range projection, fuel cost breakdown and a CO2 estimate. Click any conversion card to copy its value.

Why is L/100km lower-is-better while MPG is higher-is-better?

L/100km measures how much fuel the car needs to cover a fixed distance, so a smaller number means less fuel and greater efficiency. MPG and km/L measure how far the car goes on a fixed amount of fuel, so a larger number means more distance per liter or per gallon. Both express the same physics - they are mathematical reciprocals - but they describe it from inverted angles. Engineers prefer L/100km for fleet comparison because the metric scales linearly with fuel consumed per trip.

US vs Imperial gallon - a 20% difference

A US gallon is 3.7854 liters while an Imperial (UK) gallon is 4.5460 liters. The Imperial gallon is about 20% larger, so the same car will display a higher MPG figure under Imperial measurement. A US-spec sedan rated 30 MPG would be quoted as roughly 36 MPG in a UK brochure, even though the actual fuel use is identical. Always confirm which gallon a quoted MPG refers to before comparing two cars.

How real-world economy differs from rated economy

Official EPA, WLTP and NEDC ratings are produced under controlled lab conditions. Real-world consumption is typically 10 to 25% higher because of:

• Speed — aerodynamic drag rises with the square of speed.
• Stop-and-go traffic — engines burn more fuel during acceleration.
• Cold starts — engines need a few minutes to reach optimal temperature.
• Air conditioning — adds about 0.4 to 0.8 L/100km in summer.
• Cargo and roof racks — every 50 kg of extra weight raises consumption ~1%.
• Tire pressure — under-inflation by 20% can add ~3% to consumption.

CO2 emissions estimate

Burning one liter of gasoline emits about 2.31 kg of CO2 (well-to-wheel). One liter of diesel emits about 2.68 kg, and CNG about 1.96 kg. The CO2 figure shown by this calculator assumes gasoline; for diesel multiply the result by 1.16 and for CNG multiply by 0.85.

Frequently Asked Questions

How do I convert MPG to L/100km?

Divide 235.214583 by your MPG (US) value to get L/100km. For example, 30 MPG (US) equals 235.214583 / 30 = 7.84 L/100km. For Imperial MPG, divide 282.481 by the value instead.

What is the difference between US MPG and Imperial MPG?

A US gallon is 3.785 liters while an Imperial (UK) gallon is 4.546 liters - about 20% larger. So 30 MPG (US) is roughly 36 MPG (Imperial). Always confirm which gallon is being used before comparing fuel-economy numbers.

Why is L/100km lower-is-better while MPG is higher-is-better?

L/100km measures fuel per fixed distance, so less fuel means greater efficiency. MPG and km/L measure distance per fixed fuel, so more distance means greater efficiency. They describe the same physical quantity from inverted directions.

What is a good fuel economy?

Anything below 6 L/100km (or above 39 MPG US / 47 MPG Imperial) is considered very good for a gasoline car. Hybrids typically achieve 4-5 L/100km, compact sedans 6-8 L/100km, mid-size SUVs 9-11 L/100km, and pickup trucks 11-14 L/100km. Electric vehicles often have a gasoline-equivalent of under 2.5 L/100km.

How do I convert km/L to MPG?

Multiply km/L by 2.3521 to get MPG (US), or multiply by 2.8248 to get MPG (Imperial). For example, 15 km/L equals about 35.3 MPG (US) or 42.4 MPG (Imperial).

Does this calculator estimate CO2 emissions?

Yes. We estimate roughly 2.31 kg of CO2 per liter of gasoline burned, the typical well-to-wheel value used by the EPA and EU. Diesel emits about 2.68 kg/L, so adjust accordingly. Actual emissions depend on fuel type, driving style and vehicle condition.

Additional Resources

• Fuel efficiency - Wikipedia
• Fuel economy in automobiles - Wikipedia
• FuelEconomy.gov - U.S. Department of Energy

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