@diredko
you can take a look at the Scalability section of the documentation

The calculating scaling ratio section has an example that used to help me a lot when I first was confronted with this issue.

@Konstantin-Tokarev , thanks!
QGraphicsView::scale() works great.

@johngod Thank you so much, you're right Screen.pixelDensity would be the complete solution if it was in qml,
sifting trough the qt source i was able that it was derived from:

double pixelpermm = QGuiApplication::primaryScreen()->physicalDotsPerInch() / 25.4 //physicalDotsPerInchX() & physicalDotsPerInchY() also exist

and it seems to be correct on both my iPhone & iPad quite wel (better than all other ways I found so far)

@Lorenz thanks, but for the time being I want to stick to Qt as it is a paid sdk as soon as you go commercial

@mrjj yeah its not, but thanks though

@maximo
http://doc.qt.io/qt-5/highdpi.html
http://doc.qt.io/qt-5/qscreen.html#devicePixelRatio-prop

Looks like a bug, you should check on the bug report system