# What is the mass of an electron?

##### 1 Answer

Jan 10, 2017

As the electron is quite small, its true mass changes as it moves, and we call that the relativistic mass.

#m_"rel" = m_"rest"/sqrt(1 - v^2/c^2)#

However, as the time-independent Schrodinger equation involves what are called *stationary* states, we tend to use its **rest mass** in calculations, defined as

#m_"rest" -= m_e = 9.10938291_(40)xx10^(-31) "kg"# ,where the subscript indicates the digits past the ones to which we are certain.