QFontMetrics does not account for windows dpi scaling

[Milo]

when changing dpi scaling from 100% to 200% in Windows 10, i expect the following string to be twice as wide.

QFont font = QFont("arial", 10);
QFontMetrics fm(font);
int width = fm.width("abcdefgABCDEFG");

Strangely there is only 1 pixel difference.

100% --> width = 108 pixels
200% --> width = 109 pixels

Why is that? Do I need to compute the scaled size of the text myself?
I did enable automatic high DPI scaling in my QApplication.

QGuiApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
QApplication* app = new QApplication(temp, NULL);

Thanks