Proton–Electron Mass Ratio

How many electron masses make a proton — the number that sets the size of all chemistry.

Specifications & Metrics

symbol

mp/me

status

Measured — CODATA 2022 adjustment

value

1836.152673426 ± 3.2 × 10⁻⁸

Relative Scale in Constants

Core Principles & Analysis

• About 1836.15, so nearly all of any atom's mass sits in its nucleus.
• Hydrogen spectral lines let astronomers test whether this ratio drifts with cosmic time.
• Atoms of any kind would be unrecognizable if it differed by even a few percent.