国 内 信 封 标 准
代号     长（mm）     宽（mm）    备注
B6号    176                   125             与现行3号信封一致
DL号    220                   110             与现行5号信封一致
ZL号    230                   120              与现行6号信封一致
C5号    229                   162             与现行7号信封一致
C4号    324                    229            与现行9号信封一致

国 际 信 封 标 准
代号     长（mm） 宽（mm）     备注
C6号    162            114            新增加国际规格
B6号    176            125            与现行3号信封一致
DL号    220            110            与现行5号信封一致
ZL号    230             120           与现行6号信封一致
C5号    229            162           与现行7号信封一致
C4号    324             229          与现行9号信封一致