Standard Size and Reference Table for Pipe
Pipeline Size(British and metric comparison table)
Inch is the unit of length. 1 inch = 2.5399918 cm(cm). In or[ In] It is a unit of length used in the United Kingdom(UK, the United Kingdom(the Commonwealth). Countries such as the United States also use it. In Taiwan and Hong Kong, "in" is usually written as "in." The commonly used shorthand for inches is[ In] Or[ "] " " is a newly created word in modern times. It is pronounced as "inch". It is a word that reads two sounds in a Chinese character. Others, such as "", are pronounced as "sea", etc.. It borrows the traditional Chinese length unit "inch" and adds it. Next to show the difference.
Size:

DN15(4 in charge), DN20(6 in charge), DN25(1 inch tube), DN32(1 inch 2 tube), DN40(1 inch and a half tube), DN50(2 inch tube), DN65(2 inch and a half tube), DN80(3 inch tube), DN100 (4 inch tube), DN125(5 inch pipe), DN150(6 inch pipe), DN200(8 inch pipe), DN250(10 inch pipe) and so on.

Second, divide the inches into equal parts:
1/8 1/4 3/8 1/2 5/8 3/4 7/8 inches.
Equivalent to the usual 1 to 7, the smaller size is expressed in 1/16, 1/32, 1/64, and the unit is still in. If the denominator and the molecule can be approximately divided(such as the molecule is 2, 4, 8, 16, 32), it should be approximately divided.
The expression in inches is marked in the upper right corner, such as 1/2 "
For example, the DN25(25mm, the same below) water pipe is an imperial 1 "water pipe, which is also the previous 8 water pipe.
The DN15's water pipe is an imperial 1/2 "water pipe, which is also the previous 4-point water pipe.
For example, the DN20's water pipe is the British 3/4 "water pipe, which is also the previous 6 water pipe.
The relationship between external diameter and DN, NB is as follows: