Increase check box size not its text using QCheckbox?

I would recommend using Qt style sheet.

You can change the size of the indicator :

QCheckBox::indicator {
     width: 40px;
     height: 40px;
}

You'll have to change the image of the indicator, and provide an image with a corresponding size :

QCheckBox::indicator:checked {
     image: url(:/images/checkbox_checked.png);
}

You can also make the change using the Qt Designer and the Style Sheet editor. Right click on the QCheckbox, and select Change styleSheet.

Jérôme has given you good advice. I will just give further examples.

QCheckBox::indicator {
     width: 40px;
     height: 40px;
 }

  QCheckBox::indicator:checked
  {
    image: url(../Checkbox_checked_normal.png);
  }
  QCheckBox::indicator:unchecked
  {
    image: url(../Checkbox_unchecked_normal.png);
  }

  QCheckBox::indicator:checked:hover
  {
    image: url(../Checkbox_checked_hovered.png);
  }
  QCheckBox::indicator:unchecked:hover
  {
    image: url(../Checkbox_unchecked_hovered.png);
  }
  QCheckBox::indicator:checked:pressed
  {
    image: url(../Checkbox_checked_pressed.png);
  }
  QCheckBox::indicator:unchecked:pressed
  {
    image: url(../Checkbox_unchecked_pressed.png);
  }
  QCheckBox::indicator:checked:disabled
  {
    image: url(../Checkbox_checked_disabled.png);
  }

Pay attention to difference between url() usages. In my example I am loading images from disk rather than embedded resource system which I find more appropriate. If you start url with (:/...) it loads from embedded resource system.

Then load your style sheet as below

QFile file("your path");
bool bOpened = file.open(QFile::ReadOnly);
assert (bOpened == true);

QString styleSheet = QLatin1String(file.readAll());

qApp->setStyleSheet (styleSheet);

I hope this helps.