Proton-to-electron mass ratio = 1836.152 673 426 (dimensionless)

Name: Proton-to-electron mass ratio (mp/me) — CODATA 2022 value
Creator: NIST

Symbol: mp/me
Value: 1836.152 673 426
Unit: (dimensionless)
Uncertainty: 0.000 000 032
Copy-ready: 1836.152673426

Why almost all of an atom's mass sits in the nucleus.

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

Particle and atomic masses

Electron mass Proton mass Neutron mass Atomic mass constant (unified atomic mass unit)Proton-to-electron mass ratio

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Particle and atomic masses

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All physical constants