The numbers that are often included in the names of PEGs indicate their average molecular weights, e.g. a PEG with n=9 would have an average molecular weight of approximately 400 daltons and would be labeled PEG 400. Most PEGs include molecules with a distribution of molecular weights; i.e. they are polydisperse.
Therefore, N/Daltons is 9/400.  You can use this ratio to figure out either N or size in Dalton as long as you have either N or Dalton value.