---
title: UnitFuelEfficiency
framework: foundation
role: symbol
role_heading: Class
path: foundation/unitfuelefficiency
---

# UnitFuelEfficiency

A unit of measure for fuel efficiency.

## Declaration

```swift
class UnitFuelEfficiency
```

## Overview

Overview You typically use instances of UnitFuelEfficiency to represent specific quantities of fuel efficiency using the 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 class defines its baseUnit() as litersPer100Kilometers, and provides the following units:  |  |   |  |   |  |   |  |

## Topics

### Accessing the Base Unit

- [baseUnit()](foundation/dimension/baseunit().md)

### Accessing Predefined Units

- [milesPerImperialGallon](foundation/unitfuelefficiency/milesperimperialgallon.md)
- [litersPer100Kilometers](foundation/unitfuelefficiency/litersper100kilometers.md)
- [milesPerGallon](foundation/unitfuelefficiency/milespergallon.md)

## Relationships

### Inherits From

- [Dimension](foundation/dimension.md)

### Conforms To

- [CVarArg](swift/cvararg.md)
- [CustomDebugStringConvertible](swift/customdebugstringconvertible.md)
- [CustomStringConvertible](swift/customstringconvertible.md)
- [Equatable](swift/equatable.md)
- [Hashable](swift/hashable.md)
- [NSCoding](foundation/nscoding.md)
- [NSCopying](foundation/nscopying.md)
- [NSObjectProtocol](objectivec/nsobjectprotocol.md)
- [NSSecureCoding](foundation/nssecurecoding.md)
- [Sendable](swift/sendable.md)
- [SendableMetatype](swift/sendablemetatype.md)