A more general measure is urbanization, and by that measure Sweden is more urbanized at 88% than both Germany at 77.5% and United Kingdom at 84%.
As such nationwide population density isn’t that important, but local population density can be a very useful metric. Norway has 5,432,580 people and Óslo Norway is by far the the most populous city has 952,000 people or 17.5% of the population in the urban area at 8,500/square mile.
London has 8,961,989 people out of 63,182,000 (14.2%) in the Uk at 14,670/sq mile. And Birmingham at 1,141,816 people at 11,040/sq mi and you see the UK might have similar rates of urbanization, but it’s significantly more densely packed.
As to Stockholm Sweden, again the largest city out of 10,367,232 people in Sweden 1,605,030 million (15.5%), are living at 11,000/sq mi.
Of course this is still just an approximation. 1,000 people in a single apartment building sharing elevators adds a risk of transmission those same people living in duplex housing doesn’t.
In that context Sweden’s strategy is actually reasonable for such a low population country to attempt.