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/general/tonne**

`tonne`

**Unit name:** tonne

**Latin symbol:** t

**Display symbol:** t

**Description:** A unit of mass equal to 1000 kg using the current, or one of the historical, definitions of the SI units.

The International System of Units (SI), 1st ed. (1970) defines the tonne as "1 t = 10³ kg" with the footnote "The symbol and the unit was defined in resolution 7 at the 9th meeting of the C.G.P.M. (1948)."

In the 2019 implicit redefinition of the tonne, the kilogram in the definition refers to the 2019 kilogram SI base unit (https://schema.optimade.org/units/si/2019/named/kilogram).

- The International System of Units (SI), 1st ed. (1970) categorizes the unit as "Units used with the International System"
- The International System of Units (SI), 3rd ed. (19) changes the reference of the definition to the 1879 meeting of the CIPM page 41.
- The International System of Units (SI), 6th ed. (1991) further adds "In some English-speaking countries this unit is called ≪metric ton≫."

This is a generalized definition taken to reference the current, or one of the historical, SI unit definitions. This definition is intended for situations when it is not possible to be more precise, e.g., in contexts where data have been collected that uses different historical SI definitions.

**Resources:**

- Definition in the International System of Units (SI), 9th Edition
- Wikipedia article describing the unit

**Compatibility:** (other definitions that are covered by the above definition)

`https://schemas.optimade.org/defs/v1.2/units/si/1970/accepted/tonne`

`https://schemas.optimade.org/defs/v1.2/units/si/2019/accepted/tonne`

**JSON definition:**

```
{
"$id": "https://schemas.optimade.org/defs/v1.2/units/si/general/tonne",
"$schema": "https://schemas.optimade.org/meta/v1.2/optimade/physical_unit_definition.json",
"title": "tonne",
"symbol": "t",
"display-symbol": "t",
"alternate-symbols": [
"t"
],
"description": "A unit of mass equal to 1000 kg using the current, or one of the historical, definitions of the SI units.\n\nThe International System of Units (SI), 1st ed. (1970) defines the tonne as \"1 t = 10\u00b3 kg\" with the footnote \"The symbol and the unit was defined in resolution 7 at the 9th meeting of the C.G.P.M. (1948).\"\n\nIn the 2019 implicit redefinition of the tonne, the kilogram in the definition refers to the 2019 kilogram SI base unit (https://schema.optimade.org/units/si/2019/named/kilogram).\n\n- The International System of Units (SI), 1st ed. (1970) categorizes the unit as \"Units used with the International System\"\n- The International System of Units (SI), 3rd ed. (19) changes the reference of the definition to the 1879 meeting of the CIPM page 41.\n- The International System of Units (SI), 6th ed. (1991) further adds \"In some English-speaking countries this unit is called \u226ametric ton\u226b.\"\n\nThis is a generalized definition taken to reference the current, or one of the historical, SI unit definitions.\nThis definition is intended for situations when it is not possible to be more precise, e.g., in contexts where data have been collected that uses different historical SI definitions.",
"compatibility": [
"https://schemas.optimade.org/defs/v1.2/units/si/1970/accepted/tonne",
"https://schemas.optimade.org/defs/v1.2/units/si/2019/accepted/tonne"
],
"resources": [
{
"relation": "Definition in the International System of Units (SI), 9th Edition",
"resource-id": "https://www.bipm.org/en/publications/si-brochure"
},
{
"relation": "Wikipedia article describing the unit",
"resource-id": "https://en.wikipedia.org/wiki/Tonne"
}
],
"defining-relation": {
"base-units": [
{
"symbol": "kg",
"id": "https://schemas.optimade.org/defs/v1.2/units/si/general/kilogram"
}
],
"base-units-expression": "kg",
"scale": {
"exponent": 3
}
},
"x-optimade-definition": {
"label": "tonne_si_general",
"kind": "unit",
"format": "1.2",
"version": "1.2.0",
"name": "tonne"
}
}
```