Number of Atoms in Observable Universe

Definition
The number of atoms in the observable universe is estimated to be approximately $10^{80}$.

According to our current observations and understanding of the, the age of the Universe is estimated to be 13.787 billion years.

That means the light from the most distant galaxies has traveled 13.787 billion years to reach us.

The speed of light is $299,792,458 \text { m s}^{-1}$

This implies that the radius of the observable universe (assuming no expansion) is:

However, contemplating expansion at an average rate of $8.8 \%$ per billion years, we obtain:

This in turn implies that the volume of the Observable Universe is:

Finally, assuming there is approximately $1$ atom per cubic metre brings us to our estimate of approximately $10^{80}$ atoms in the Observable Universe.