Speed of light in vacuum = 299 792 458 m·s⁻¹

Name: Speed of light in vacuum (c) — CODATA 2022 value
Creator: NIST

Symbol: c
Value: 299 792 458
Unit: m·s⁻¹
Uncertainty: exact (by definition)
Copy-ready: 299792458

Defines the metre. Light in a material always travels slower, by a factor equal to the refractive index.

NIST, Fundamental Physical Constants — Complete Listing (2022 CODATA adjustment), retrieved 2026-07-26.

Calculators that use c

Wavelength Snell's Law

The seven SI defining constants

Caesium-133 hyperfine transition frequency Speed of light in vacuum Planck constant Elementary charge Boltzmann constant Avogadro constant Luminous efficacy of 540 THz radiation

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UsePhysics. "Speed of light in vacuum — 299 792 458 m·s⁻¹." UsePhysics.com. https://usephysics.com/reference/speed-of-light. Value from the 2022 CODATA adjustment (NIST). Accessed [date].