Joule symbol

A capital J, the SI unit symbol for the joule.

ScientificMathematicalEngineering & technicalStandard profile

Meanings

J is the SI symbol for the joule, the derived unit of energy, work and heat. Food labelling states energy in kilojoules alongside calories.

Officially standardisedVerified fact
Denotes the joule, the SI derived unit of energy, work and quantity of heat.
Contexts: Mathematics
Common modern usageVerified fact
Covers energy, work and heat with one unit, which is the physical claim behind it: mechanical work and thermal energy are the same quantity and are measured the same way.
Contexts: Mathematics
Common modern usageVerified fact
Appears as kJ on food packaging, where energy content is commonly given in kilojoules alongside the older kilocalorie.
Contexts: Packaging

Visual description

The capital Latin letter J: a vertical stroke descending from the cap height and hooking to the left at its foot.

Symmetry: none
Orientation: upright

Used alongside: Watt symbol
Energy and the rate at which it is delivered.

Confidence

IdentityHigh confidence: High confidence because the identity is defined by a current official standard, but multiple independent sources agree.
Historical originModerate confidence: Moderate confidence because the historical origin is documented in encyclopedic references, but multiple independent sources agree, 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, but multiple independent sources agree.
Visual matchHigh confidence: High confidence because the visual match is documented in encyclopedic references, but multiple independent sources agree.

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.
SI derived unit
Wikipedia · retrieved 2026-07-31
Tertiary reference. Used for origin narrative and for units the SI does not define, never for an official-definition claim.
Guide for the Use of the International System of Units (SI), NIST Special Publication 811
National Institute of Standards and Technology · retrieved 2026-07-31
A national metrology institute's guidance on applying the SI, including symbol formatting. Authoritative for usage rules in the United States; it interprets the SI rather than defining it.
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

J is the SI symbol for the joule, the derived unit of energy, work and heat. Food labelling states energy in kilojoules alongside calories.

Officially standardisedVerified fact

Denotes the joule, the SI derived unit of energy, work and quantity of heat.

Contexts: Mathematics

Common modern usageVerified fact

Covers energy, work and heat with one unit, which is the physical claim behind it: mechanical work and thermal energy are the same quantity and are measured the same way.

Contexts: Mathematics

Common modern usageVerified fact

Appears as kJ on food packaging, where energy content is commonly given in kilojoules alongside the older kilocalorie.

Contexts: Packaging

Confidence

IdentityHigh confidence: High confidence because the identity is defined by a current official standard, but multiple independent sources agree.
Historical originModerate confidence: Moderate confidence because the historical origin is documented in encyclopedic references, but multiple independent sources agree, 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, but multiple independent sources agree.
Visual matchHigh confidence: High confidence because the visual match is documented in encyclopedic references, but multiple independent sources agree.

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.
SI derived unit
Wikipedia · retrieved 2026-07-31
Tertiary reference. Used for origin narrative and for units the SI does not define, never for an official-definition claim.
Guide for the Use of the International System of Units (SI), NIST Special Publication 811
National Institute of Standards and Technology · retrieved 2026-07-31
A national metrology institute's guidance on applying the SI, including symbol formatting. Authoritative for usage rules in the United States; it interprets the SI rather than defining it.
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

Meanings

Visual description

Related & commonly confused symbols

Meanings

Visual description

Related & commonly confused symbols