How do you calculate the mass of the universe?
Taking in to account the rapid rate of expansion of the universe and the number of photons that have travelled from the beginning or estimated age of the universe we get a number of roughly 92 billion light years. This value, however, will be affected by many factors we are still unsure about and things such as redshift. For example, redshift will affect the distance a photon may travel as photons lose energy as they are redshifted, leading to an increase or decrease in the value of the size of the universe.
The link below goes into more detail regarding redshift and how it affects photons