What is the fine-structure constant (α)?

The fine-structure constant is α = 7.2973525693e-3 ≈ 1/137 (dimensionless, uncertainty ±1.1e-12). Its inverse is 137.035999084.

Key facts

Frequently asked questions

What is the value of the fine-structure constant?

α = 7.2973525693e-3, approximately 1/137, a dimensionless measure of the strength of the electromagnetic interaction.

Why is 1/137 famous?

Because 1/α ≈ 137.036, a pure number whose value sets the strength of electromagnetism and has no known explanation.

Is α exact?

No. It is measured with a tiny uncertainty of ±1.1e-12 and is among the most precisely known constants.

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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