Rest mass of a photon is
According to Einstein's quantum theory light propagates in the form of packets i.e. quanta of energy, which is called photon.
The rest mass of photons is being zero. It can be shown, according to the relativity theory of light.
According to the relativistic theory equation, the mass of the photon is computed as:
m=m0√1−v2c2
m0=m√1−v2c2
when v=0;
So m0=0
Where m0 is the rest mass of the Photon.