Explanation of Φ，DN，Inch(")

Inch(")：

The inch (") is a common unit of specification in the American system, used for steel pipes, valves, flanges, elbows, pumps, tees, etc. For example, a specification might be 3".

The term "inch" (abbreviated as "in.") originally meant "thumb" in Dutch,with one inch was the length of one thumb joint. Of course, the length of a person's thumb naturally varies. In the 14th century, King Edward II of England established the "standard legal inch." It was defined as the length of three of the largest barley grains from the middle of an ear of barley, placed end to end.

Generally, 1" = 2.54 cm = 25.4 mm.

DN：

DN is a common specification unit in the Chinese and European systems, similarly used to designate the specifications of pipes, valves, flanges, pipe fittings, and pumps, such as DN300.

DN refers to the nominal diameter of a pipe (also known as the nominal bore). It is important to note that this is neither the outer diameter nor the inner diameter, but rather an average value between the two, known as the mean internal diameter.

Φ：

Φ is a universal symbol denoting the outer diameter dimension of pipes, elbows, round steel, and other materials,which can also be referred to as the diameter. For example, Φ609.6 mm refers to an outer diameter of 609.6 mm. This symbol is commonly used in valve applications, particularly for clamp connections.

Interconnection Among the Three

First, " and DN have nearly identical meanings, both essentially representing the nominal bore, indicating the size of the specification. Φ serves to combine the two.

For example: If a steel pipe is specified as DN250, the same pipe would be labeled 10" in inches. Is there a connection between them?

The answer is yes. Generally, you can convert whole-inch dimensions to DN by multiplying by 25. For instance:

1" × 25 = DN25 2" × 25 = DN50 4" × 25 = DN100

However, there are exceptions. For example, 3" × 25 = 75, which rounds to DN80. There are also inch dimensions with fractions or decimals like 1/2", 3/4", 1-1/4", 1-1/2", 2-1/2", 3-1/2",these can't be calculated that way, but the calculations are roughly the same,they're mostly standard values:

1/2"=DN15

3/4"=DN20 

1-1/4"=DN32 

1-1/2"=DN40 

2-1/2"=DN65