XML Purchase order no of item display in PDF output

Hello Sir,

    I creating purchase order report in rdf and save the output into XML and create the RTF document. i am using <xsl:variable name="no_of_lines_per_page" select="number(4)"/>    it is working fine when 1 item description 1 or 2 lines. when the item description more than 4 lines the page alignment go to next page.

For Example.

Item Description one or two lines page preak is correct

  item no           Description                                                                     QTY             Value

   123             PRESSURE GAUGE 0-16KG/CM2 6" DIAL BOTTOM ENTRY,SS

                               MATERIAL,BOURDON TYPE 232.50,160MM DIA WITH                                        1                         100

    125              PRESSURE GAUGE 0-6KG/CM2 6" DIAL BOTTOM ENTRY,SS

                               PRESSURE GAUGE 0-6KG/CM2 6" DIAL BOTTOM ENTRY,SS                               2                        150