<!--
{
  "availability" : [
    "iOS: 10.0.0 -",
    "iPadOS: 10.0.0 -",
    "macCatalyst: 13.1.0 -",
    "macOS: 10.12.0 -",
    "tvOS: 10.0.0 -",
    "visionOS: 1.0.0 -",
    "watchOS: 3.0.0 -"
  ],
  "documentType" : "symbol",
  "framework" : "Foundation",
  "identifier" : "/documentation/Foundation/UnitFuelEfficiency",
  "metadataVersion" : "0.1.0",
  "role" : "Class",
  "symbol" : {
    "kind" : "Class",
    "modules" : [
      "Foundation"
    ],
    "preciseIdentifier" : "c:objc(cs)NSUnitFuelEfficiency"
  },
  "title" : "UnitFuelEfficiency"
}
-->

# UnitFuelEfficiency

A unit of measure for fuel efficiency.

```
class UnitFuelEfficiency
```

## Overview

You typically use instances of [`UnitFuelEfficiency`](/documentation/Foundation/UnitFuelEfficiency) to represent specific quantities of fuel efficiency using the [`NSMeasurement`](/documentation/Foundation/NSMeasurement) class.

### Fuel Efficiency

Fuel efficiency corresponds to the thermal efficiency of a process that converts the chemical potential energy of a fuel into kinetic energy. Fuel efficiency can be expressed by SI derived units in terms of cubic meters per meter (m3/m), but is more commonly expressed in terms of liters per kilometer (L/km) and miles per gallon (mpg).

The [`UnitFuelEfficiency`](/documentation/Foundation/UnitFuelEfficiency) class defines its [`baseUnit()`](/documentation/Foundation/Dimension/baseUnit()) as [`litersPer100Kilometers`](/documentation/Foundation/UnitFuelEfficiency/litersPer100Kilometers), and provides the following units:

|Name                     |Method                                                                                           |Symbol |
|-------------------------|-------------------------------------------------------------------------------------------------|-------|
|Liters Per 100 Kilometers|``doc://com.apple.foundation/documentation/Foundation/UnitFuelEfficiency/litersPer100Kilometers``|L/100km|
|Miles Per Gallon         |``doc://com.apple.foundation/documentation/Foundation/UnitFuelEfficiency/milesPerGallon``        |mpg    |
|Miles Per Imperial Gallon|``doc://com.apple.foundation/documentation/Foundation/UnitFuelEfficiency/milesPerImperialGallon``|mpg    |

## Topics

### Accessing the Base Unit

[`baseUnit()`](/documentation/Foundation/Dimension/baseUnit())

Returns the base unit.

### Accessing Predefined Units

[`milesPerImperialGallon`](/documentation/Foundation/UnitFuelEfficiency/milesPerImperialGallon)

The miles per imperial gallon unit of fuel efficiency.

[`litersPer100Kilometers`](/documentation/Foundation/UnitFuelEfficiency/litersPer100Kilometers)

The liters per 100 kilometers unit of fuel efficiency.

[`milesPerGallon`](/documentation/Foundation/UnitFuelEfficiency/milesPerGallon)

The miles per gallon unit of fuel efficiency.


---

Copyright &copy; 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)