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/2019/accepted/tonne**

`tonne`

**Unit name:** tonne

**Latin symbol:** t

**Display symbol:** t

**Description:** A unit of mass defined as 1000 kg, with kilogram defined according to the 2019 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≫."

**Resources:**

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

**JSON definition:**

```
{
"$id": "https://schemas.optimade.org/defs/v1.2/units/si/2019/accepted/tonne",
"$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 defined as 1000 kg, with kilogram defined according to the 2019 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.\"",
"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/2019/base/kilogram"
}
],
"base-units-expression": "kg",
"scale": {
"exponent": 3
}
},
"x-optimade-definition": {
"label": "tonne_si_2019_accepted",
"kind": "unit",
"format": "1.2",
"version": "1.2.0",
"name": "tonne"
}
}
```