This page documents an OPTIMADE Unit Definition. See https://schemas.optimade.org/ for more information.

**ID: https://schemas.optimade.org/defs/v1.2/units/si/1983/temporary/hectare**

`hectare`

**Unit name:** hectare

**Latin symbol:** ha

**Display symbol:** ha

**Description:** A unit of area equal to 1000 square meters (1 hm²), with meter defined according to the 1983 SI base unit.

The hectare unit appears in the International System of Units (SI), 1st ed. (1970) defined as "1 ha = 1 hm² = 10⁴ m²" with the footnote "This unit and its symbol were adopted by the International Committee in 1879 (Proces-Verbaux C.I.P.M., 1879, p. 41)."

- The International System of Units (SI), 1st ed. (1970) categorizes the unit as "units in use temporarily".
- The International System of Units (SI), 5th ed. (1985) add the clarification that the unit is "used to express agrarian areas."
- The International System of Units (SI), 7th ed. (1998) changes the categorisation to "Other non-SI units currently accepted for use with the International System."

The hectare unit was implicitly redefined via the redefinition of the metre at the 17th CGPM meeting (1983), resolution 1.

**Resources:**

- Definition in the International System of Units (SI), 9th Edition
- Redefinition of the metre at the 17th CGPM meeting (1983), resolution 1
- Wikipedia article describing the unit

**JSON definition:**

```
{
"$id": "https://schemas.optimade.org/defs/v1.2/units/si/1983/temporary/hectare",
"$schema": "https://schemas.optimade.org/meta/v1.2/optimade/physical_unit_definition.json",
"title": "hectare",
"symbol": "ha",
"display-symbol": "ha",
"description": "A unit of area equal to 1000 square meters (1 hm\u00b2), with meter defined according to the 1983 SI base unit.\n\nThe hectare unit appears in the International System of Units (SI), 1st ed. (1970) defined as \"1 ha = 1 hm\u00b2 = 10\u2074 m\u00b2\" with the footnote \"This unit and its symbol were adopted by the International Committee in 1879 (Proces-Verbaux C.I.P.M., 1879, p. 41).\"\n\n- The International System of Units (SI), 1st ed. (1970) categorizes the unit as \"units in use temporarily\".\n- The International System of Units (SI), 5th ed. (1985) add the clarification that the unit is \"used to express agrarian areas.\"\n- The International System of Units (SI), 7th ed. (1998) changes the categorisation to \"Other non-SI units currently accepted for use with the International System.\"\n\nThe hectare unit was implicitly redefined via the redefinition of the metre at the 17th CGPM meeting (1983), resolution 1.",
"resources": [
{
"relation": "Definition in the International System of Units (SI), 9th Edition",
"resource-id": "https://www.bipm.org/en/publications/si-brochure"
},
{
"relation": "Redefinition of the metre at the 17th CGPM meeting (1983), resolution 1",
"resource-id": "https://www.bipm.org/en/committees/cg/cgpm/17-1983/resolution-1"
},
{
"relation": "Wikipedia article describing the unit",
"resource-id": "https://en.wikipedia.org/wiki/Hectare"
}
],
"defining-relation": {
"base-units": [
{
"symbol": "m",
"id": "https://schemas.optimade.org/defs/v1.2/units/si/1983/base/metre"
}
],
"base-units-expression": "m^2",
"scale": {
"exponent": 4
}
},
"x-optimade-definition": {
"label": "hectare_si_1983_temporary",
"kind": "unit",
"format": "1.2",
"version": "1.2.0",
"name": "hectare"
}
}
```