How to Convert Pixels to Millimeters

If you need to convert pixel value to millimeters (inches, centimeters, etc.) use the code provided here.

The code uses the API function GetDeviceCaps to get the metrics you need.
 

procedure PixelsPerMM( canvas: TCanvas; var x, y: single) ;
var
    H:HDC;
    hres,vres,
    hsiz,vsiz:integer;
begin
    H:=canvas.handle;
    hres := GetDeviceCaps(H,HORZRES) ; {display width in pixels}
    vres := GetDeviceCaps(H,VERTRES) ; {display height in pixels}
    hsiz := GetDeviceCaps(H,HORZSIZE) ; {display width in mm}
    vsiz := GetDeviceCaps(H,VERTSIZE) ; {display height in mm}
    x := hres/hsiz;
    y := vres/vsiz;
end;