QCAD 3 TP1 cannot export to PNG (or any other bitmap format). QCAD 2 lets set width and height in pixels of the file to be created. The drawing is then scaled proportionally to fit that. Leaving the height value empty will crash QCAD 2. QCAD 2 will also pad the image with an unspecified value that gets (both absolutely and relatively) smaller when the size increases…

QCAD 2 interface is simple and should meet most users needs. It would be nice to calculate the missing value, if only width or height is set. Some padding might be necessary only when antialiasing is done on export.

Setting scale and DPI instead would require more thinking on users side…