With our 9.9 million people Sweden is still about a million short of the population of Italy in the 1500s. Back in 1570 we were only about 900,000 though. And far fewer in the so called viking period.
Norway is estimated to have had only 80,000 people at the height of the viking period, growing to some 200,000 at the end of it, while Denmark had 500,000 in the beginning and near a million at the end. Sweden seems to have had about 600,000 in the middle of the 1300s. About half the people would have been children. And of course roughly half also female or male.
These early numbers are educated guesswork though as no contemporary census was ever made.