# Units Reference
URL: /reference/units

Searchable table of all 2,134 unit constants in openhtf.util.units — name, UNECE code and suffix — with how to attach units to measurements and dimensions and how to look a unit up by string.

`openhtf.util.units` defines one `UnitDescriptor` constant per unit of measure, generated from the UNECE Recommendation 20 code list. Attach one to a measurement with `.with_units()`; it is stored in the record as `{name, code, suffix}` so downstream tools can label and convert values.

`units.Unit()` resolves a unit from its name, suffix or code, and `.with_units()` accepts a string directly:

Two special constants: `units.NONE` (no unit) and `units.NO_DIMENSION` (a ratio or count that has a unit conceptually but no dimension).

Quantity

Constants

Voltage

`VOLT`, `MILLIVOLT`, `MICROVOLT`, `KILOVOLT`

Current

`AMPERE`, `MILLIAMPERE`, `MICROAMPERE`

Resistance

`OHM`, `KILOOHM`, `MEGAOHM`, `MILLIOHM`

Power

`WATT`, `MILLIWATT`, `KILOWATT`, `DECIBEL_MILLIWATTS`, `WATT_HOUR`

Frequency

`HERTZ`, `KILOHERTZ`, `MEGAHERTZ`, `GIGAHERTZ`

Time

`SECOND`, `MILLISECOND`, `MICROSECOND`, `MINUTE`, `HOUR`

Temperature

`DEGREE_CELSIUS`, `DEGREE_FAHRENHEIT`, `KELVIN`

Length

`METRE`, `MILLIMETRE`, `MICROMETRE_MICRON`, `INCH`

Pressure

`PASCAL`, `KILOPASCAL`, `BAR_UNIT_OF_PRESSURE`, `POUND_PER_SQUARE_INCH_GAUGE`, `POUND_PER_SQUARE_INCH_ABSOLUTE`

Data

`BYTE`, `KILOBYTE`, `MEGABYTE`, `GIGABYTE`, `BIT_PER_SECOND`

Ratio

`PERCENT`, `DECIBEL`, `PART_PER_MILLION`

Angle

`DEGREE_UNIT_OF_ANGLE`, `RADIAN`

Spellings follow the UNECE names, which are not always what you would guess (`KILOOHM`, `MEGAOHM`, `DECIBEL_MILLIWATTS`, `MICROMETRE_MICRON`, `BAR_UNIT_OF_PRESSURE`); use the filter below to confirm before you type.

Units also label the axes of a multi-dimensional measurement. Pass `UnitDescriptor`s or `htf.Dimension(description=..., unit=...)`:

`code` is the UNECE common code — stable across languages and tools, which is why OpenHTF uses it rather than a free-text unit string. JSON format →

<Card title="Measurements" href="/measurements" description="Validators, options and multi-dimensional data." />

<Card title="Validators reference" href="/reference/validators" description="Limits that go with the units." />