If the whole observable Universe is as big as planet Earth, how big would Earth be? If the whole observable Universe is as big as planet Earth, how big would Earth be?
The radius of the observable Universe is 41.5billion light years (ref).
A light year is $9.5\cdot10^{12}$ km.
The radius of the Earth is 6371 km.


So the answer is $6371 km \cdot \frac{6371 km}{41.5\cdot10^9\cdot9.5\cdot10^{12}km} = 1.03\cdot10^{-16}km = \underline{\underline{1.03\cdot10^{-13}m}}$.

The size of the atoms are $\approx 10^{-10}m$.