# Physical quantities

Length, mass, temperature, energy and other measured amounts.

## Topics

| Page | What it covers |
|---|---|
| [Physical quantities](/docs/physical-quantities.md) | A quantity type holds a measured amount, such as a length, a mass, a temperature or a file's size. |

## Types

| Type | What it is |
|---|---|
| [`Length`](/docs/types/type-length.md) | A length or distance: `5km`, `45cm`, `3inch` or `2metre`. |
| [`Area`](/docs/types/type-area.md) | An area: `12sqm` or `2ha`. |
| [`Volume`](/docs/types/type-volume.md) | A volume: `500ml` or `2litre`. |
| [`Angle`](/docs/types/type-angle.md) | An angle: `90deg` or `1.5rad`. |
| [`Mass`](/docs/types/type-mass.md) | A mass or weight: `250g`, `2.5kg` or `500mcg`. |
| [`Pressure`](/docs/types/type-pressure.md) | A pressure: `1013hPa`. |
| [`Energy`](/docs/types/type-energy.md) | An amount of energy: `2kWh` or `250kcal`. |
| [`Power`](/docs/types/type-power.md) | A rate of energy use: `3kW`. |
| [`Temperature`](/docs/types/type-temperature.md) | A temperature: `21degC`, `70degF` or `300kelvin`. |
| [`TemperatureDifference`](/docs/types/type-temperature-difference.md) | The gap between two temperatures, so 5 °C warmer isn't the same as 5 °C. |
| [`Speed`](/docs/types/type-speed.md) | A speed: `30mph` or `100kmh`. |
| [`Frequency`](/docs/types/type-frequency.md) | How often something happens per second: `50Hz` or `2.4GHz`. |
| [`Voltage`](/docs/types/type-voltage.md) | An electrical voltage: `230V`. |
| [`Current`](/docs/types/type-current.md) | An electric current: `500mA`. |
| [`Illuminance`](/docs/types/type-illuminance.md) | How much light falls on a surface: `500lx`. |
| [`SoundLevel`](/docs/types/type-sound-level.md) | How loud something is: `60dB`. |
| [`Concentration`](/docs/types/type-concentration.md) | A mass in a volume: `5mgL` or `1gL`. |