Avogadro Constant

The exact number of constituent particles in one mole of substance, defining the SI mole.

Specifications & Metrics

symbol

N_A

status

Exact — SI defining constant (2019)

value

6.02214076 × 10²³ mol⁻¹

Relative Scale in Constants

Core Principles & Analysis

• Exactly 6.02214076 × 10²³ entities per mole since the 2019 SI redefinition.
• Named for Amedeo Avogadro, whose 1811 hypothesis held that equal gas volumes contain equal molecule counts.
• Counting the atoms in near-perfect silicon-28 spheres measured it precisely enough to justify fixing it.

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