Kilogram symbol

The two-letter symbol kg, the SI unit symbol for the kilogram.

Also known as: Kilo

ScientificMathematicalEngineering & technicalStandard profile

Meanings

kg is the SI symbol for the kilogram, the base unit of mass, and the only base unit whose name already contains a prefix — which is why smaller multiples are built on the gram rather than on the kilogram.

Officially standardisedVerified fact
Denotes the kilogram, the SI base unit of mass.
Contexts: Mathematics
Common modern usageVerified fact
Is the only SI base unit whose name and symbol already carry a prefix, so decimal multiples are formed on the gram — milligram, microgram — rather than by stacking a second prefix onto the kilogram.
Contexts: Mathematics
Common modern usageVerified fact
Was redefined in 2019 in terms of the Planck constant, replacing the international prototype kilogram — the last physical artefact any SI unit depended on.
Contexts: Mathematics

Visual description

Two lower-case Latin letters side by side: a k with a vertical stem and two diagonal strokes, followed by a g with a round bowl and a descending tail.

Symmetry: none
Orientation: upright

Confidence

IdentityHigh confidence: High confidence because the identity is defined by a current official standard.
Historical originModerate confidence: Moderate confidence because the historical origin is documented in encyclopedic references, but early or supporting evidence is limited, but the regional or cultural match to this specific claim is not precise.
Current useHigh confidence: High confidence because the current use is defined by a current official standard.
Visual matchHigh confidence: High confidence because the visual match is documented in encyclopedic references.

Sources

SI base units
Bureau International des Poids et Mesures · retrieved 2026-07-31
The seven base units and their symbols as published by the defining body. A summary page: the SI Brochure remains the full instrument.
The International System of Units (SI), 9th edition
Bureau International des Poids et Mesures · retrieved 2026-07-31
The defining document for SI unit names and symbols, including the capitalisation and spacing rules. It defines units; it says nothing about how a symbol is encoded in a character set, and nothing about non-SI units except where it lists those accepted for use with the SI.

Last reviewed 2026-08-01

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Units of measurement and their symbols

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Meanings

Officially standardisedVerified fact

Denotes the kilogram, the SI base unit of mass.

Contexts: Mathematics

Common modern usageVerified fact

Is the only SI base unit whose name and symbol already carry a prefix, so decimal multiples are formed on the gram — milligram, microgram — rather than by stacking a second prefix onto the kilogram.

Contexts: Mathematics

Common modern usageVerified fact

Was redefined in 2019 in terms of the Planck constant, replacing the international prototype kilogram — the last physical artefact any SI unit depended on.

Contexts: Mathematics

Confidence

IdentityHigh confidence: High confidence because the identity is defined by a current official standard.
Historical originModerate confidence: Moderate confidence because the historical origin is documented in encyclopedic references, but early or supporting evidence is limited, but the regional or cultural match to this specific claim is not precise.
Current useHigh confidence: High confidence because the current use is defined by a current official standard.
Visual matchHigh confidence: High confidence because the visual match is documented in encyclopedic references.

Sources

SI base units
Bureau International des Poids et Mesures · retrieved 2026-07-31
The seven base units and their symbols as published by the defining body. A summary page: the SI Brochure remains the full instrument.
The International System of Units (SI), 9th edition
Bureau International des Poids et Mesures · retrieved 2026-07-31
The defining document for SI unit names and symbols, including the capitalisation and spacing rules. It defines units; it says nothing about how a symbol is encoded in a character set, and nothing about non-SI units except where it lists those accepted for use with the SI.

Last reviewed 2026-08-01