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# UnitMass

A unit of measure for mass.

```
class UnitMass
```

## Overview

You typically use instances of [`UnitMass`](/documentation/Foundation/UnitMass) to represent specific quantities of mass using the [`NSMeasurement`](/documentation/Foundation/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`](/documentation/Foundation/UnitMass) class defines its [`baseUnit()`](/documentation/Foundation/Dimension/baseUnit()) as [`kilograms`](/documentation/Foundation/UnitMass/kilograms), and provides the following units, which [`UnitConverterLinear`](/documentation/Foundation/UnitConverterLinear) converters initialize with the given coefficients:

|Name       |Method                                                                     |Symbol|Coefficient |
|-----------|---------------------------------------------------------------------------|------|------------|
|Kilograms  |``doc://com.apple.foundation/documentation/Foundation/UnitMass/kilograms`` |kg    |`1.0`       |
|Grams      |``doc://com.apple.foundation/documentation/Foundation/UnitMass/grams``     |g     |`0.001`     |
|Decigrams  |``doc://com.apple.foundation/documentation/Foundation/UnitMass/decigrams`` |dg    |`0.0001`    |
|Centigrams |``doc://com.apple.foundation/documentation/Foundation/UnitMass/centigrams``|cg    |`0.00001`   |
|Milligrams |``doc://com.apple.foundation/documentation/Foundation/UnitMass/milligrams``|mg    |`0.000001`  |
|Micrograms |``doc://com.apple.foundation/documentation/Foundation/UnitMass/micrograms``|µg    |`1e-9`      |
|Nanograms  |``doc://com.apple.foundation/documentation/Foundation/UnitMass/nanograms`` |ng    |`1e-12`     |
|Picograms  |``doc://com.apple.foundation/documentation/Foundation/UnitMass/picograms`` |pg    |`1e-15`     |
|Ounces     |``doc://com.apple.foundation/documentation/Foundation/UnitMass/ounces``    |oz    |`0.0283495` |
|Pounds     |``doc://com.apple.foundation/documentation/Foundation/UnitMass/pounds``    |lb    |`0.453592`  |
|Stones     |``doc://com.apple.foundation/documentation/Foundation/UnitMass/stones``    |st    |`0.157473`  |
|Metric Tons|``doc://com.apple.foundation/documentation/Foundation/UnitMass/metricTons``|t     |`1000`      |
|Short Tons |``doc://com.apple.foundation/documentation/Foundation/UnitMass/shortTons`` |ton   |`907.185`   |
|Carats     |``doc://com.apple.foundation/documentation/Foundation/UnitMass/carats``    |ct    |`0.0002`    |
|Ounces Troy|``doc://com.apple.foundation/documentation/Foundation/UnitMass/ouncesTroy``|oz t  |`0.03110348`|
|Slugs      |``doc://com.apple.foundation/documentation/Foundation/UnitMass/slugs``     |slug  |`14.5939`   |

## Topics

### Accessing the Base Unit

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

Returns the base unit.

### Accessing Predefined Units

[`kilograms`](/documentation/Foundation/UnitMass/kilograms)

The kilograms unit of mass.

[`grams`](/documentation/Foundation/UnitMass/grams)

The grams unit of mass.

[`decigrams`](/documentation/Foundation/UnitMass/decigrams)

The decigrams unit of mass.

[`centigrams`](/documentation/Foundation/UnitMass/centigrams)

The centigrams unit of mass.

[`milligrams`](/documentation/Foundation/UnitMass/milligrams)

The milligrams unit of mass.

[`micrograms`](/documentation/Foundation/UnitMass/micrograms)

The micrograms unit of mass.

[`nanograms`](/documentation/Foundation/UnitMass/nanograms)

The nanograms unit of mass.

[`picograms`](/documentation/Foundation/UnitMass/picograms)

The picograms unit of mass.

[`ounces`](/documentation/Foundation/UnitMass/ounces)

The ounces unit of mass.

[pounds](/documentation/Foundation/1808594-pounds)

Returns the pounds unit of mass.

[`poundsMass`](/documentation/Foundation/UnitMass/pounds)

The pounds unit of mass.

[`stones`](/documentation/Foundation/UnitMass/stones)

The stone unit of mass.

[`metricTons`](/documentation/Foundation/UnitMass/metricTons)

The metric tons unit of mass.

[`shortTons`](/documentation/Foundation/UnitMass/shortTons)

The short tons unit of mass.

[`carats`](/documentation/Foundation/UnitMass/carats)

The carats unit of mass.

[`ouncesTroy`](/documentation/Foundation/UnitMass/ouncesTroy)

The ounces troy unit of mass.

[`slugs`](/documentation/Foundation/UnitMass/slugs)

The slugs unit of mass.

## Relationships

### Conforms To

[`CustomStringConvertible`](/documentation/Swift/CustomStringConvertible)

[`NSCopying`](/documentation/Foundation/NSCopying)

[`Sendable`](/documentation/Swift/Sendable)

[`SendableMetatype`](/documentation/Swift/SendableMetatype)

[`Hashable`](/documentation/Swift/Hashable)

[`NSCoding`](/documentation/Foundation/NSCoding)

[`CustomDebugStringConvertible`](/documentation/Swift/CustomDebugStringConvertible)

[`Equatable`](/documentation/Swift/Equatable)

[`NSSecureCoding`](/documentation/Foundation/NSSecureCoding)

[`NSObjectProtocol`](/documentation/ObjectiveC/NSObjectProtocol)

[`CVarArg`](/documentation/Swift/CVarArg)

### Inherits From

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

---

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