LCD Monitor DPI at Native Resolution

Relative pixel density for a given resolution
calculated this way:
DPI = sqrt( Wpx^2+Hpx^2 )

1680x1050@20" --> 99dpi
1600x1200@21" --> 95dpi
1680x1050@22" --> 90dpi
1920x1200@24" --> 94dpi

using google as my calculator (e.x. for 1920x1200#24")