---
title: UnitMass
framework: foundation
role: symbol
role_heading: Class
path: foundation/unitmass
---

# UnitMass

A unit of measure for mass.

## Declaration

```swift
class UnitMass
```

## Overview

Overview You typically use instances of UnitMass to represent specific quantities of mass using the NSMeasurement class. Mass Mass is a fundamental property of matter that causes it to resist a force accelerating it. The SI unit for mass is the kilogram (kg), which defined in terms of the mass of the international prototype kilogram. The UnitMass class defines its baseUnit() as kilograms, 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

- [kilograms](foundation/unitmass/kilograms.md)
- [grams](foundation/unitmass/grams.md)
- [decigrams](foundation/unitmass/decigrams.md)
- [centigrams](foundation/unitmass/centigrams.md)
- [milligrams](foundation/unitmass/milligrams.md)
- [micrograms](foundation/unitmass/micrograms.md)
- [nanograms](foundation/unitmass/nanograms.md)
- [picograms](foundation/unitmass/picograms.md)
- [ounces](foundation/unitmass/ounces.md)
- [pounds](foundation/1808594-pounds.md)
- [pounds](foundation/unitmass/pounds.md)
- [stones](foundation/unitmass/stones.md)
- [metricTons](foundation/unitmass/metrictons.md)
- [shortTons](foundation/unitmass/shorttons.md)
- [carats](foundation/unitmass/carats.md)
- [ouncesTroy](foundation/unitmass/ouncestroy.md)
- [slugs](foundation/unitmass/slugs.md)

### Initializers

- [init(forLocale:usage:)](foundation/unitmass/init(forlocale:usage:).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

### Mass, Weight, and Force

- [UnitPressure](foundation/unitpressure.md)