Bohr Radius

$$a_0=\frac{4\pi {ϵ}_0{\hslash }^2}{m_e{e}^2}=\frac{\hslash }{m_{e}c\alpha }=5.2946551599\times 10^{-11}\text{ m}$$

where

• ${ϵ}_0$ is the permitivity of free space
• $\hslash$ is the Reduced Planck Constant
• $m_e$ is the mass of an Electron
• $e$ is the Elementary Charge
• $c$ is the Speed of Light
• $\alpha$ is the Fine Structure Constant

See also

Bohr Model