What is the proton-to-electron mass ratio?

The proton-electron mass ratio is m_p/m_e = 1836.15267343 (dimensionless, uncertainty ±1.1e-7).

Key facts

Frequently asked questions

How many times heavier is a proton than an electron?

The proton is 1836.15267343 times more massive than the electron.

Is the proton-electron mass ratio exact?

No. It is measured with a relative uncertainty around 6e-11, making it very precisely known.

Why does this ratio matter?

It is a dimensionless constant whose value influences atomic structure and is tested against possible variation over cosmic time.

Related pages

• Speed of light
• Planck constant
• Reduced Planck constant
• Avogadro constant
• Boltzmann constant
• Molar gas constant
• Elementary charge
• Gravitational constant

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