Relativistic Energy

$$E_{\text{total}}=K+E_0=\gamma m{c}^2$$

where $E_0=m{c}^2$ is the “rest energy”; literally the energy when the object is at rest

$$K=(\gamma -1)m{c}^2=\gamma m{c}^2-m{c}^2=\gamma m{c}^2-E_0$$ $$p^2{c}^2=E_{\text{total}}^2-E_0^2$$

See Also

Relativistic Momentum