How big would an SSTO be?

If someone were to build an SSTO using realistic assumptions about mass
ratios and available power systems, how big a vehicle would be needed to
send (say) three people and a modest amount of cargo into LEO? I have
seen Apollo capsules in museums, so I am using them as my baseline.
Would such a thing be the size of a regular jetliner? Or the new Airbus
super jumbo jet? Or are we talking about a Zeppelin on steroids?

Also, how would these things scale? If we wanted to increase the crew
from three to four, would the vehicle size go up by a third? Or more?

Thanks

David Cornell