I know that a photon cannot have mass. I know that a photon does carry energy, however. So, just for fun I used E=mc2, to find out how much mass a photo would have. This was mainly just to play around with the equation, but I found the answer interesting. 1.11265005605e-31 kilograms. That is the mass of a single photon, even though I know its not. What I don't know is why its not.