Detect font (Small or Large) is in use

Use GetDeviceCaps function with LOGPIXELSX parameter to detect what font (large or small) is in use.

procedure TForm1.Button1Click(Sender: TObject);
var
  DC: hDC;
begin
  DC:=GetDC(Form1.Handle);
  if GetDeviceCaps(DC, LOGPIXELSX) = 96 then
    Label1.Caption:='Small font is in use';
  if GetDeviceCaps(DC, LOGPIXELSX) = 120 then
    Label1.Caption:='Large font is in use';
  ReleaseDC(Form1.Handle, DC);
end;