The return value of HSSFSheet.getDefaultColumnWidth is 8. According the document "get the width (in units of 1/256th of a character width ) ", it should be 8*256=2048.
HSSFSheet.getDefaultColumnWidth() returns the width measured in characters. HSSFSheet.getColumnWidth() returns the width in units of 1/256th of a character width. Regards, Yegor