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# UnitSpeed

A unit of measure for speed.

```
class UnitSpeed
```

## Overview

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

### Speed

Speed is the magnitude of velocity, or the rate of change of position. Speed can be expressed by SI derived units in terms of meters per second (m/s), and is also commonly expressed in terms of kilometers per hour (km/h) and miles per hour (mph).

The [`UnitSpeed`](/documentation/Foundation/UnitSpeed) class defines its [`baseUnit()`](/documentation/Foundation/Dimension/baseUnit()) as [`metersPerSecond`](/documentation/Foundation/UnitSpeed/metersPerSecond), and provides the following units, which are initialized using [`UnitConverterLinear`](/documentation/Foundation/UnitConverterLinear) converters with the specified coefficients:

|Name               |Method                                                                             |Symbol|Coefficient|
|-------------------|-----------------------------------------------------------------------------------|------|-----------|
|Meters Per Second  |``doc://com.apple.foundation/documentation/Foundation/UnitSpeed/metersPerSecond``  |m/s   |`1.0`      |
|Kilometers Per Hour|``doc://com.apple.foundation/documentation/Foundation/UnitSpeed/kilometersPerHour``|km/h  |`0.277778` |
|Miles Per Hour     |``doc://com.apple.foundation/documentation/Foundation/UnitSpeed/milesPerHour``     |mph   |`0.44704`  |
|Knots              |``doc://com.apple.foundation/documentation/Foundation/UnitSpeed/knots``            |kn    |`0.514444` |

The base unit is [`metersPerSecond`](/documentation/Foundation/UnitSpeed/metersPerSecond) and is accessed via [`baseUnit()`](/documentation/Foundation/Dimension/baseUnit()) on the [`Dimension`](/documentation/Foundation/Dimension) protocol.

## Topics

### Accessing the Base Unit

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

Returns the base unit.

### Accessing Predefined Units

[`metersPerSecond`](/documentation/Foundation/UnitSpeed/metersPerSecond)

The meter per second unit of speed.

[`kilometersPerHour`](/documentation/Foundation/UnitSpeed/kilometersPerHour)

The kilometers per hour unit of speed.

[`milesPerHour`](/documentation/Foundation/UnitSpeed/milesPerHour)

The miles per hour unit of speed.

[`knots`](/documentation/Foundation/UnitSpeed/knots)

The knots unit of speed.


---

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