<p>How do I create a button control (with <code>CreateWindow</code> of a <code>BUTTON</code> window class) that has a standard system-wide size (especially height) that's consistent with the rest of Windows applications?
I should of course take DPI into account and probably other settings.</p>

<blockquote>
  <p><strong>Remark:</strong> Using <code>USE_CW_DEFAULT</code> for width and height results in a 0, 0 size button, so that's not a solution.</p>
</blockquote>

This is what MSDN has to say:
Design Specifications and Guidelines - Visual Design: Layout
.
The default size of a button is 50x14 DLUs, which can be calculated to pixels using the examples shown for
GetDialogBaseUnits
.
The
MapDialogRect
function seems to do the calculation for you.