product_labels/data/report_paperformat.xml

<?xml version="1.0" encoding="utf-8"?>
<openerp>
    <data>
        <record id="paperformat_product_label" model="report.paperformat">
            <field name="name">Product Label</field>
            <field name="default" eval="True"/>
            <field name="format">custom</field>
            <field name="page_height">40</field>
            <field name="page_width">65</field>
            <field name="orientation">Portrait</field>
            <field name="margin_top">1</field>
            <field name="margin_bottom">1</field>
            <field name="margin_left">2</field>
            <field name="margin_right">2</field>
            <field name="header_line" eval="False" />
            <field name="header_spacing">0</field>
            <field name="dpi">300</field>
        </record>
    </data>
</openerp>