---
title: UnitDuration
framework: foundation
role: symbol
role_heading: Class
path: foundation/unitduration
---

# UnitDuration

A unit of measure for a duration of time.

## Declaration

```swift
class UnitDuration
```

## Overview

Overview You typically use instances of UnitDuration to represent specific quantities of planar angle using the NSMeasurement class. Duration Duration is a quantity of time. The SI unit for time is the second (sec), which is defined in terms of the radioactivity of a cesium-133 atom. Duration is also commonly expressed in terms of minutes (min) and hours (hr). note: Use the NSDateComponents class to represent quantities of calendrical units, such as days, weeks, months, and years. The UnitDuration class defines its baseUnit() as seconds, and provides the following units, which UnitConverterLinear converters initialize with the given coefficients:  |  |  |   |  |  |   |  |  |   |  |  |

## Topics

### Accessing the Base Unit

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

### Accessing Predefined Units

- [hours](foundation/unitduration/hours.md)
- [minutes](foundation/unitduration/minutes.md)
- [seconds](foundation/unitduration/seconds.md)
- [milliseconds](foundation/unitduration/milliseconds.md)
- [microseconds](foundation/unitduration/microseconds.md)
- [nanoseconds](foundation/unitduration/nanoseconds.md)
- [picoseconds](foundation/unitduration/picoseconds.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)

## See Also

### Time and Motion

- [UnitAcceleration](foundation/unitacceleration.md)
- [UnitFrequency](foundation/unitfrequency.md)
- [UnitSpeed](foundation/unitspeed.md)