Comment by m132

That really depends on the context. Open your browser's Developer Tools and you'll see logical sizes everywhere. Android, which in my opinion has the best scaling model, and where the PPI wildly varies from device to device, nearly always operates on logical sizes. Windows, GNOME, and KDE on the other hand tend to give you measurements in physical pixels. macOS is a mix and match; Preview and QuickTime tell you the physical resolutions, Interface Builder and display preferences will only show logical dimensions.