A Comparison Table for Pipe Nominal Diameter and Outer Diameter

The nominal diameter is the size to express the piping systems and all piping accessories by digital, nominal diameter is just a reference with a convenient round integers, it is not a strict relationship for maching size. Nominal diameter "DN" was followed by a number sign.

Nominal diameter (nominal diameter), also known as the average diameter. This is because the thickness of metal pipe is very thin. It is almost the same for pipe outer diameter and inner diameter. So we take the average as nominal diameter to call it.

The nominal diameter is not outer diameter, also not inner diameter, but the approximation of ordinary steel pipe diameter size. Each nominal diameter corresponding to an outer diameter, and the inner diameter is not the same because the pipe thickness is different.
The nominal diameter is to express by metric “mm”, also available inch “in”. The piping accessories can be also named the nominal diameter.

A Comparison Table for Pipe Nominal Diameter and Outer Diameter.
No.	DN (Nominal Diameter)	OD Outer Diameter
No.	DN (Nominal Diameter)	Weld Pipe	SMLS Pipe	Spiral Steel Pipe	UPVC Pipe	PP-R Pipe	PB Pipe	Aluminum Plastic Pipe	Cast Iron Pipe for Water	HDPE Pipe
1	15	21.3			20	20	20	20
2	20	26.8	28		25	25	25	25
3	25	33.5	32		32	32	32	32
4	32	42.3	38		40	40	40	40
5	40	48	48		50	50	50	50
6	50	60	57		63	63	63	63	50	50
7	65	75.5	76		75	75	75	75		75
8	80	88.5	89		90	90	90	90	75
9	100	114	108		110	110	110	110	100	110
10	125	140	133		140	140	140	140	125
11	150	165	159		160	160	160	160	150	160
12	200		219	219	225	225	225	225	200	200
13	250		273	273	280	280	280	280
14	300		325	325	315	315	315	315
15	350		377	377
16	400		426	426
17	450		480	480
18	500		530	530
19	600		630	630

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