Fuel Economy Calculator

Fuel economy measures how efficiently a vehicle uses fuel, expressed as the distance traveled per unit of fuel or the fuel consumed per unit of distance. Different countries use different units, which can make comparing vehicles across markets confusing. This calculator bridges that gap by instantly converting between the three most common fuel economy standards used worldwide.

The Three Fuel Economy Units

Miles per gallon (MPG) is the standard in the United States and the United Kingdom. It measures how many miles a vehicle can travel on one gallon of fuel. A higher MPG number indicates better fuel efficiency. In the US, the EPA provides both city and highway MPG ratings, as well as a combined figure.

Liters per 100 kilometers (L/100km) is used across Europe, Australia, and much of the rest of the world. Unlike MPG, it measures fuel consumption rather than distance — a lower L/100km number means better efficiency. For example, a car rated at 6 L/100km uses 6 liters of fuel to travel 100 kilometers.

Kilometers per liter (km/L) is commonly used in Japan, India, and several other Asian countries. Like MPG, a higher km/L number means better efficiency. It provides an intuitive measurement of how far you can travel on a single liter of fuel.

How to Convert Between Units

The mathematical relationship between these units is straightforward. To convert MPG to L/100km, divide 235.215 by the MPG value. For example, 30 MPG equals 235.215 ÷ 30 = 7.84 L/100km. To go from L/100km to km/L, simply divide 100 by the L/100km value: 7.84 L/100km equals 100 ÷ 7.84 = 12.76 km/L.

The constant 235.215 comes from the conversion between US gallons, liters, miles, and kilometers. One US gallon equals 3.78541 liters, and one mile equals 1.60934 kilometers. Multiplying these gives 3.78541 × 100 ÷ 1.60934 ≈ 235.215.

What Is Good Fuel Economy?

What counts as good fuel economy depends heavily on the vehicle type. For compact cars and sedans, 30 MPG (7.8 L/100km) or better is considered good, while 40 MPG (5.9 L/100km) or higher is excellent. For SUVs and crossovers, 25 MPG (9.4 L/100km) is respectable. Full-size trucks and vans typically range from 15 to 22 MPG (10.7 to 15.7 L/100km).

Hybrid vehicles routinely achieve 40 to 60 MPG (3.9 to 5.9 L/100km), while plug-in hybrids can exceed 100 MPGe when running on electric power. The best non-hybrid conventional vehicles on the market today achieve around 35 to 40 MPG combined.

Factors That Affect Fuel Economy

Real-world fuel economy often differs from official ratings by 10 to 20 percent. Driving behavior is the single largest factor — aggressive acceleration and high-speed driving can reduce efficiency by 15 to 33 percent. Maintaining a steady speed between 55 and 65 mph (90 to 105 km/h) typically yields the best fuel economy for most vehicles.

Vehicle maintenance also plays a significant role. Properly inflated tires can improve fuel economy by up to 3 percent, while a clean air filter and fresh engine oil contribute to optimal combustion efficiency. External factors like cold weather, headwinds, hilly terrain, and heavy loads can all reduce fuel economy. Air conditioning use typically costs 1 to 4 MPG depending on conditions.

Regional Differences in Fuel Economy Standards

It is important to note that US MPG and UK MPG are different because they use different gallon sizes. A US gallon is 3.785 liters, while an Imperial gallon is 4.546 liters. This means a vehicle rated at 30 US MPG would be rated at about 36 UK MPG. This calculator uses US gallons, which is the more internationally recognized standard.

Government fuel economy testing procedures also vary by region. The US EPA cycle, European WLTP, and Japanese JC08/WLTC tests all use different driving patterns and conditions, which can produce different ratings for the same vehicle. WLTP figures tend to be closer to real-world performance than older NEDC ratings, while EPA figures are generally considered the most conservative.