管材的直径根据所属管材的材质不同，其意义也不一样，金属管道如钢管，铁管等所指的管直径是指内径，而PE管，PPR管等都是指外径，标注上DN指内径，DE指外径，我们常说的4分管，6分管，1寸管是英制的标准，4分管是 G1/2英寸的俗称，6分管也就是G3/4的意思

   公称通径DN/mm        俗     称              相当管螺纹/in           外径 DE/mm

               6                        1分管                       1/8                                 10

               8                        2分管                       1/4                                 

              10                      3分管                       3/8                             14或者17

              15                      4分管                       1/2                             18或者22

              20                      6分管                        3/4                             25或者27

              25                      1寸管                         1                                32或者34