Fuel Economy Calculator

What Is Fuel Economy?

Fuel economy describes how efficiently a vehicle turns fuel into distance traveled. The same vehicle can have its efficiency reported in different ways depending on the country, manufacturer, website, or vehicle specification sheet.

In the United States, miles per gallon (MPG) is common. Many countries use liters per 100 kilometers (L/100 km), while kilometers per liter (km/L) is also used in many markets. The important detail is that these measurements do not all move in the same direction: higher MPG and km/L are generally better, while lower L/100 km is generally better.

MPG vs. L/100 km

MPG tells you how many miles a vehicle can travel using one gallon. Because the denominator is fuel and the numerator is distance, a larger MPG number generally indicates greater fuel efficiency.

L/100 km reverses the perspective. It tells you how many liters are needed to travel 100 kilometers. A vehicle using 6 L/100 km therefore generally uses less fuel for the same distance than one using 9 L/100 km.

How to Convert MPG to L/100 km

To convert US miles per gallon to liters per 100 kilometers, use the standard conversion relationship:

For example, a vehicle rated at 25 MPG converts to approximately 9.41 L/100 km.

How to Convert L/100 km to MPG

The reverse conversion uses the same constant:

If a vehicle uses 8 L/100 km, the equivalent is approximately 29.40 MPG.

Fuel Economy Conversion Reference

US MPG vs. UK MPG

A US gallon and an Imperial gallon are not the same size. This matters when converting vehicle specifications from US sources to UK or other Imperial-gallon sources. The calculator therefore treats MPG (US) and MPG (UK) as separate measurements instead of silently treating them as interchangeable.

If a vehicle specification simply says “MPG,” check the source before comparing it with another number. Mixing US and Imperial MPG can make a vehicle appear more or less efficient than it really is.

How to Read km/L

Kilometers per liter works in the same general direction as MPG: higher numbers mean more distance can be traveled from one liter of fuel. For example, 10 km/L means the vehicle travels about 10 kilometers for every liter consumed under the stated conditions.

The relationship with L/100 km is especially simple:

Why Two Vehicles Can Have Different Fuel Economy

Engine design, vehicle weight, aerodynamics, gearing, tire choice, hybrid technology, driving conditions, and driving behavior can all affect fuel consumption. Official ratings are useful for comparisons, but your actual results can differ.

If you have your own distance and fuel-use records, use the measured fuel use to calculate your observed efficiency. You can then convert that result here into another unit system.

Fuel Economy and Trip Cost

Fuel economy becomes much more useful when it is connected to fuel price and distance. A vehicle with better efficiency generally needs less fuel for the same trip, but the actual savings depend on how far you drive and what you pay for fuel.

Use the trip fuel cost tool to turn an efficiency number into an estimated trip expense. For ownership decisions, fuel is only one part of the picture; financing, depreciation and other costs also matter.

Example: Comparing Two Vehicles

Imagine two vehicles traveling the same 300-mile route. One gets 20 MPG and the other gets 30 MPG. The 20 MPG vehicle needs approximately 15 gallons, while the 30 MPG vehicle needs about 10 gallons.

At a hypothetical $3.50 per gallon, the difference is about $17.50 for that 300-mile trip. Repeated commuting can make a similar efficiency difference much more significant over a year.

Fuel Economy vs. Fuel Consumption

“Fuel economy” and “fuel consumption” are closely related, but the wording can change how a number should be interpreted. MPG and km/L describe distance obtained from fuel. L/100 km and L/100 mi describe fuel required for a fixed distance.

This is why a lower L/100 km number can represent a more efficient vehicle even though a lower number might seem worse at first glance.

Real-World Fuel Economy

Your actual fuel economy can differ from an advertised or laboratory rating. Traffic, speed, terrain, weather, vehicle load, tire pressure, idling, air conditioning, and driving style can all influence fuel consumption.

For a useful personal benchmark, calculate your efficiency over several fill-ups rather than relying on one short trip. A longer observation period can reduce the effect of unusual traffic or weather.

Fuel Economy Calculator FAQs