>Does anyone know how I can convert the grid's column width from pixels to inches?

convert to twips -- 1440 twips equals 1 inch:

************************************************************************************************
* Function to Convert from Pixels to Twips
*
* Parameters:  
*     pnPixels       Value to convert to twips
*     pcDirection    Screen direction; 'H' for horizontal and 'V' for vertical
*
* Returns:
*     Twips value
*
FUNCTION PixelsToTwips
LPARAMETERS pnPixels, pcDirection
LOCAL lhDeviceHdl, lnPixelsPerInch
#DEFINE LOGPIXELSX  88
#DEFINE LOGPIXELSY  90
DECLARE LONG GetDeviceCaps IN "gdi32"  LONG hdc,  LONG nIndex
DECLARE LONG ReleaseDC     IN "user32" LONG hwnd, LONG hdc
DECLARE LONG GetDC         IN "user32" LONG hwnd
lhDeviceHdl = GetDC(0)
DO CASE
   CASE pcDirection = "H"        && Horizontal
      lnPixelsPerInch = GetDeviceCaps(lhDeviceHdl,LOGPIXELSX)
   CASE pcDirection = "V"        && Vertical
      lnPixelsPerInch = GetDeviceCaps(lhDeviceHdl,LOGPIXELSY)
ENDCASE
lhDeviceHdl = ReleaseDC(0,lhDeviceHdl)
RETURN pnPixels * 1440 / lnPixelsPerInch
ENDFUNC

In the above code on the RETURN statement, do not multiply by 1440 to get inches returned. You have to be sensitive to the vertical and horizontal directions as these can provide different values.