Avogadro constant symbol

A capital N with subscript A, the number of entities in a mole.

Also known as: Avogadro's number, N with a subscript A

ScientificMathematicalStandard profile

Meanings

N_A is the number of entities in one mole, exact since 2019. It is a counting factor rather than a measured property of nature — which is why it could be fixed by definition at all.

Common modern usageVerified fact
Denotes the number of elementary entities in one mole of substance.
Contexts: Mathematics, Laboratory
Officially standardisedVerified fact
Has had an exact value, 6.022 140 76 × 10²³ per mole, since 2019, when the mole was redefined as a fixed count rather than as a mass of carbon-12.
Contexts: Mathematics, Laboratory
Common modern usageVerified fact
Is a counting factor rather than a measured property of nature, which is why it could be fixed by definition where the gravitational constant cannot.
Contexts: Mathematics, Laboratory

Visual description

A capital Latin letter N in italic type followed by a small capital A set as a subscript below the baseline.

Symmetry: none
Orientation: upright

Used alongside: Mole symbol
The mole is defined as this number of entities.

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

Avogadro constant
Wikipedia · retrieved 2026-08-01
Tertiary reference. Used for what a symbol denotes in ordinary scientific practice and for which fields reuse it, never for a claim that any body assigns the letter its meaning.
Gravitational constant
Wikipedia · retrieved 2026-08-01
Tertiary reference. Used for what a symbol denotes in ordinary scientific practice and for which fields reuse it, never for a claim that any body assigns the letter its meaning.
The SI defining constants
Bureau International des Poids et Mesures · retrieved 2026-08-01
The seven constants whose exact values define the SI since 2019. Cited for the fact that a constant's value is fixed by definition rather than measured — a claim about the unit system, not about the notation.
CODATA Internationally Recommended Values of the Fundamental Physical Constants
NIST / CODATA Task Group on Fundamental Constants · retrieved 2026-08-01
Authoritative for the recommended value and uncertainty of a physical constant, and for whether that value is exact by definition or measured. It fixes values; it does not decide which letter denotes which quantity, and no record cites it for a symbol's meaning.
Physical constant
Wikipedia · retrieved 2026-08-01
Tertiary reference. Used for what a symbol denotes in ordinary scientific practice and for which fields reuse it, never for a claim that any body assigns the letter its meaning.

Last reviewed 2026-07-31

Part of

Physical constants and quantity symbols

Help improve this page

Meanings

N_A is the number of entities in one mole, exact since 2019. It is a counting factor rather than a measured property of nature — which is why it could be fixed by definition at all.

Common modern usageVerified fact

Denotes the number of elementary entities in one mole of substance.

Contexts: Mathematics, Laboratory

Officially standardisedVerified fact

Has had an exact value, 6.022 140 76 × 10²³ per mole, since 2019, when the mole was redefined as a fixed count rather than as a mass of carbon-12.

Contexts: Mathematics, Laboratory

Common modern usageVerified fact

Is a counting factor rather than a measured property of nature, which is why it could be fixed by definition where the gravitational constant cannot.

Contexts: Mathematics, Laboratory

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

Avogadro constant
Wikipedia · retrieved 2026-08-01
Tertiary reference. Used for what a symbol denotes in ordinary scientific practice and for which fields reuse it, never for a claim that any body assigns the letter its meaning.
Gravitational constant
Wikipedia · retrieved 2026-08-01
Tertiary reference. Used for what a symbol denotes in ordinary scientific practice and for which fields reuse it, never for a claim that any body assigns the letter its meaning.
The SI defining constants
Bureau International des Poids et Mesures · retrieved 2026-08-01
The seven constants whose exact values define the SI since 2019. Cited for the fact that a constant's value is fixed by definition rather than measured — a claim about the unit system, not about the notation.
CODATA Internationally Recommended Values of the Fundamental Physical Constants
NIST / CODATA Task Group on Fundamental Constants · retrieved 2026-08-01
Authoritative for the recommended value and uncertainty of a physical constant, and for whether that value is exact by definition or measured. It fixes values; it does not decide which letter denotes which quantity, and no record cites it for a symbol's meaning.
Physical constant
Wikipedia · retrieved 2026-08-01
Tertiary reference. Used for what a symbol denotes in ordinary scientific practice and for which fields reuse it, never for a claim that any body assigns the letter its meaning.

Last reviewed 2026-07-31

Meanings

Visual description

Related & commonly confused symbols

Meanings

Visual description

Related & commonly confused symbols