> For the complete documentation index, see [llms.txt](https://ess-dive.gitbook.io/sample-id-and-metadata/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://ess-dive.gitbook.io/sample-id-and-metadata/term-lists/units.md).

# units

Here is a subset of controlled unit terms for Environmental Systems Science (ESS) samples, using existing ontology terms from Units Ontology (UO) link to ontology term details (IRI for term).

Please provide feedback on any additional unit terms needed.

| **Unit category** | **Unit Label**    | **UO ID**                                   |
| ----------------- | ----------------- | ------------------------------------------- |
| length            | meter             | <http://purl.obolibrary.org/obo/UO_0000008> |
| length            | centimeter        | <http://purl.obolibrary.org/obo/UO_0000015> |
| length            | millimeter        | <http://purl.obolibrary.org/obo/UO_0000016> |
| length            | micrometer        | <http://purl.obolibrary.org/obo/UO_0000017> |
| area              | square meter      | <http://purl.obolibrary.org/obo/UO_0000080> |
| area              | square centimeter | <http://purl.obolibrary.org/obo/UO_0000081> |
| area              | square millimeter | <http://purl.obolibrary.org/obo/UO_0000082> |
| area              | square micrometer | <http://purl.obolibrary.org/obo/UO_0010001> |
| mass              | kilogram          | <http://purl.obolibrary.org/obo/UO_0000009> |
| mass              | gram              | <http://purl.obolibrary.org/obo/UO_0000021> |
| mass              | milligram         | <http://purl.obolibrary.org/obo/UO_0000022> |
| mass              | microgram         | <http://purl.obolibrary.org/obo/UO_0000023> |
| mass              | nanogram          | <http://purl.obolibrary.org/obo/UO_0000024> |
| mass              | picogram          | <http://purl.obolibrary.org/obo/UO_0000025> |
| volume            | cubic meter       | <http://purl.obolibrary.org/obo/UO_0000096> |
| volume            | cubic centimeter  | <http://purl.obolibrary.org/obo/UO_0000097> |
| volume            | cubic decimeter   | <http://purl.obolibrary.org/obo/UO_0000100> |
| volume            | milliliter        | <http://purl.obolibrary.org/obo/UO_0000098> |
| volume            | liter             | <http://purl.obolibrary.org/obo/UO_0000099> |
| volume            | nanoliter         | <http://purl.obolibrary.org/obo/UO_0000102> |
| volume            | picoliter         | <http://purl.obolibrary.org/obo/UO_0000103> |