Pipe Schedule Number is the standard method to define the thickness of the pipes used in Process Plants.

Standardization of wrought steel Pipe schedule and pipe sizes begin with the mass production era. At that time pipes are available in only three sizes standard weight (STD), extra-strong (XS), and double extra-strong (XXS), based on the iron pipe size (IPS) system.

With the modernizing of various industries and the use of pipes in different pressure and temperature condition, three sizes are not sufficient to meet the requirement. This will result in the concept of the schedule number that combines wall thickness and diameter of the pipe.

In current practice, pipe size defines with two sets of number

  1. Pipe bore/nominal diameter
  2. Pipe schedule which is nothing but wall thickness of the pipe.

What is Nominal Pipe Size?

Nominal pipe size (NPS) is the number that defines the size of the pipe. For example, when you say 6” pipe, the 6” is the nominal size of that pipe. However, for the pipe sizes, NPS 14 and above Outside Diameter is the same as NPS. To understand this concept, you have to learn the way pipes are manufactured.

Manufacturing of NPS ⅛ (DN 6) to NPS 12 (DN 300) pipe is based on fixed outside diameter (OD). So, any increase in wall thickness, the inside diameter (ID) of the pipe decrease. So the NPS will be somewhere in-between OD & ID of the pipe.

Manufacturing of NPS 14 (DN350) and above pipe OD is corresponding to the Nominal Size of a pipe. With below example, you have more clarity of the concept.

OD in
Inch
OD in
mm
Thickness in
Inch
Thickness in
mm
ID in
Inch
ID in
mm
For NPS 2 Schedule 40 pipe
2.375 60.3 0.154 3.91 2.067 52.5
For NPS 14 Schedule 40 pipe
14 350 0.438 11.13 13.124 333.3

From the above table, you can see that for NPS 2, Pipe ID is near to pipe NPS and for NPS 14 pipe OD is same as NPS.

4 sch 80 pipe schedule

You can easily convert inch dimension to mm by multiplying it with 25.4 and rounding as follow;

  1. Outside diameter above 16 inches rounded to nearest 1 mm
  2. Outside diameter 16 inches and below rounded to nearest 0.1 mm
  3. Pipe wall thickness are rounded to nearest 0.01 mm

What is Pipe NB (Nominal Bore)?

NPS is frequently referred as an NB (Nominal Bore). As such, there is no difference between NB and NPS. NB is also an American way to refer pipe dimensions. I have also seen that when pipe dimensions are shown in mm (DN) people refer pipe sizes in NB. So when someone says 25nb pipe or 50nb pipe basically they are talking about DN.

What is DN (Diameter Nominal) Pipe Sizes?

DN or Diameter Nominal is an International designation (SI or Matric Designator) and also a European equivalent of NPS to show pipe sizes. Here, you have to note that DN shows pipe sizes differently than NPS.

2” pipe is simply mentioned as DN 50. You can get any NPS to DN by multiplying it with 25. Check the below table for easy understanding. There is no change in other dimensions when you use DN.

Nominal Pipe Size Diameter Nominal Nominal Pipe Size Diameter Nominal
NPS (inches) DN (mm) NPS (inches) DN (mm)
1/8 6 20 500
1/4 8 22 550
3/8 10 24 600
1/2 15 26 650
3/4 20 28 700
1 25 30 750
1 ¼ 32 32 800
1 ½ 40 36 900
2 50 40 1000
2 ½ 65 42 1050
3 80 44 1100
3 ½ 90 48 1200
4 100 52 1300
5 125 56 1400
6 150 60 1500
8 200 64 1600
10 250 68 1700
12 300 72 1800
14 350 76 1900
16 400 80 2000
18 450 Based on ASME B36.10

From this table, you can see that initially pipe size increase by ¼ than ½ and then by 1”. Form 6” to 42”, it increases by 2” step and after that in 4”.

What is Pipe Schedule?

The pipe schedule is the way pipe wall thickness is mentioned. To simplify the ordering of the pipe ASME committee has developed Schedule Number which is based on modified Barlow’s wall thickness formula.

Definition of Schedule Number: The schedule number indicates approximate value of the expression 1000 x P/S where P is the service pressure and S is the allowable stress, both expressed in pounds per square inch.

You can see the pipe schedule calculation formula as below;

Schedule number = P/S

  • P is the service pressure in (psi)
  • S is the allowable stress in (psi)

So, what does schedule 40 means?

Schedule 40 is nothing but a pipe thickness designator. In simple word you can say that for a given material, schedule 40 pipe can withstand a certain amount of pressure.

Now, can you tell me which is thicker schedule 40 or 80 pipe?

Schedule 80 pipe is thicker than schedule 40 pipe. Look at the above formula of schedule number, allowable stress for material at a given temperature is fixed. That means with an increase in service pressure schedule number will increase which is a pipe wall thickness designator.

Pipe Schedule for Stainless Steel Pipe

Cost of stainless steel pipe is much higher than carbon steel pipe. Due to corrosion resistance properties of stainless steel, advancement of high alloy stainless steel and fusion welding less thickness pipe can be work satisfactorily without fear of early failure.

To reduces the cost of material ASME has introduced different schedule numbers for stainless steel pipe and fittings. Under ASME B36.19 Schedule no with “S” suffix is introduced for SS pipe. Example- 10S

Standard Pipe Schedule as per ASME B36.10 and B36.19

Refer to the table give below that summarized the available schedule numbers for carbon steel and stainless steel pipe based on ASME B36.10 and B36.19.

For Carbon Steel and Wrought iron Pipe as per ASME B36.10 5, 10, 20, 30, 40, 60, 80, 100, 120, 140, 160, STD, XS, XXS
For Stainless Steel Pipe as per ASME B36.19 5S, 10S, 40S, 80S

Please note following;

  • STD (Standard) and Schedule 40 has the same thickness up to NPS 10 (DN 250)
  • Above NPS 10 STD has a wall thickness of 3/8 in. (9.53 mm)
  • XS has the same thickness as Schedule 80 for up to NPS 8 (DN 200)
  • Above NPS 8 XS have a wall thickness of ½ in. (12.5 mm)

NPS Pipe Size Chart in Inch

Nominal Pipe Size Chart – In Inches
Size in Inch OD 5 5s 10 10s 20 30 40 40s Std 60 80 80s XS 100 120 140 160 XXS Size in Inch
1/8 0.405 0.049 0.049 0.068 0.068 0.068 0.095 0.095 0.095 1/8
1/4 0.54 0.065 0.065 0.088 0.088 0.088 0.119 0.119 0.119 1/4
3/8 0.675 0.065 0.065 0.073 0.091 0.091 0.091 0.126 0.126 0.126 3/8
1/2 0.84 0.065 0.065 0.083 0.083 0.095 0.109 0.109 0.109 0.147 0.147 0.147 0.188 0.294 1/2
3/4 1.05 0.065 0.065 0.083 0.083 0.095 0.113 0.113 0.113 0.154 0.154 0.154 0.219 0.308 3/4
1 1.315 0.065 0.065 0.109 0.109 0.114 0.133 0.133 0.133 0.179 0.179 0.179 0.25 0.358 1
1 1/4 1.66 0.065 0.065 0.109 0.109 0.117 0.14 0.14 0.14 0.191 0.191 0.191 0.25 0.382 1 1/4
1 1/2 1.9 0.065 0.065 0.109 0.109 0.125 0.145 0.145 0.145 0.2 0.2 0.2 0.281 0.4 1 1/2
2 2.375 0.065 0.065 0.109 0.109 0.125 0.154 0.154 0.154 0.218 0.218 0.218 0.344 0.436 2
2 1/2 2.875 0.083 0.083 0.12 0.12 0.188 0.203 0.203 0.203 0.276 0.276 0.276 0.375 0.552 2 1/2
3 3.5 0.083 0.083 0.12 0.12 0.188 0.216 0.216 0.216 0.3 0.3 0.3 0.438 0.6 3
3 1/2 4 0.083 0.083 0.12 0.12 0.188 0.226 0.226 0.226 0.318 0.318 0.318 0.636 3 1/2
4 4.5 0.083 0.083 0.12 0.12 0.188 0.237 0.237 0.237 0.337 0.337 0.337 0.438 0.531 0.674 4
5 5.563 0.109 0.109 0.134 0.134 0.258 0.258 0.258 0.375 0.375 0.375 0.5 0.625 0.75 5
6 6.625 0.109 0.109 0.134 0.134 0.28 0.28 0.28 0.432 0.432 0.432 0.562 0.719 0.864 6
8 8.625 0.109 0.109 0.148 0.148 0.25 0.277 0.322 0.322 0.322 0.406 0.5 0.5 0.5 0.594 0.719 0.812 0.906 0.875 8
10 10.75 0.134 0.134 0.165 0.165 0.25 0.307 0.365 0.365 0.365 0.5 0.594 0.5 0.5 0.719 0.844 1 1.125 1 10
12 12.75 0.156 0.156 0.18 0.18 0.25 0.33 0.406 0.375 0.375 0.562 0.688 0.5 0.5 0.844 1 1.125 1.312 1 12
14 14 0.156 0.156 0.25 0.188 0.312 0.375 0.438 0.375 0.375 0.594 0.75 0.5 0.5 0.938 1.094 1.25 1.406 14
16 16 0.165 0.165 0.25 0.188 0.312 0.375 0.5 0.375 0.375 0.656 0.844 0.5 0.5 1.031 1.219 1.438 1.594 16
18 18 0.165 0.165 0.25 0.188 0.312 0.438 0.562 0.375 0.375 0.75 0.938 0.5 0.5 1.156 1.375 1.562 1.781 18
20 20 0.188 0.188 0.25 0.218 0.375 0.5 0.594 0.375 0.375 0.812 1.031 0.5 0.5 1.281 1.5 1.75 1.969 20
22 22 0.188 0.188 0.25 0.218 0.375 0.5 0.375 0.875 1.125 0.5 1.375 1.625 1.875 2.125 22
24 24 0.218 0.218 0.25 0.25 0.375 0.562 0.688 0.375 0.375 0.969 1.219 0.5 0.5 1.531 1.812 2.062 2.344 24
26 26 0.312 0.5 0.375 0.5
28 28 0.312 0.5 0.625 0.375 0.5
30 30 0.25 0.25 0.312 0.312 0.5 0.625 0.375 0.5
32 32 0.312 0.5 0.625 0.688 0.375 0.5
34 34 0.312 0.5 0.625 0.688 0.375 0.5
36 36 0.312 0.5 0.625 0.75 0.375 0.5
38 38 0.375 0.5
40 40 0.375 0.5
42 42 0.375 0.5
44 44 0.375 0.5
46 46 0.375 0.5
48 48 0.375 0.5
Size in Inch OD 5 5s 10 10s 20 30 40 40s Std 60 80 80s XS 100 120 140 160 XXS Size in Inch
ASME B36.10M-2015: Welded and Seamless Wrought Steel Pipe
ASME B36.19M-2004: Stainless Steel Pipe (For 5S,10S,40S and 80S)
Don’t get confused between 3 1/2 inch nominal with 3.5 inch OD, 4″ nominal with 4.000″ OD

NPS Pipe Size Chart in MM

Nominal Pipe Size Chart – Nominal Pipe Dimension in Millimeter (mm)
DN in mm OD 5 5s 10 10s 20 30 40 40s Std 60 80 80s XS 100 120 140 160 XXS DN in mm
6 10.3 1.24 1.24 1.73 1.73 1.73 2.41 2.41 2.41
8 13.7 1.65 1.65 2.24 2.24 2.24 3.02 3.02 3.02
10 17.1 1.65 1.65 1.85 2.31 2.31 2.31 3.2 3.2 3.2
15 21.3 1.65 1.65 2.11 2.11 2.41 2.77 2.77 2.77 3.73 3.73 3.73 4.78 7.47
20 26.7 1.65 1.65 2.11 2.11 2.41 2.87 2.87 2.87 3.91 3.91 3.91 5.56 7.82
25 33.4 1.65 1.65 2.77 2.77 2.9 3.38 3.38 3.38 4.55 4.55 4.55 6.35 9.09
32 42.2 1.65 1.65 2.77 2.77 2.97 3.56 3.56 3.56 4.85 4.85 4.85 6.35 9.7
40 48.3 1.65 1.65 2.77 2.77 3.18 3.68 3.68 3.68 5.08 5.08 5.08 7.14 10.16
50 60.3 1.65 1.65 2.77 2.77 3.18 3.91 3.91 3.91 5.54 5.54 5.54 8.74 11.07
65 73 2.11 2.11 3.05 3.05 4.78 5.16 5.16 5.16 7.01 7.01 7.01 9.53 14.02
80 88.9 2.11 2.11 3.05 3.05 4.78 5.49 5.49 5.49 7.62 7.62 7.62 11.13 15.24
90 101.6 2.11 2.11 3.05 3.05 4.78 5.74 5.74 5.74 8.08 8.08 8.08 16.15
100 114.3 2.11 2.11 3.05 3.05 4.78 6.02 6.02 6.02 8.56 8.56 8.56 11.13 13.49 17.12
125 141.3 2.77 2.77 3.4 3.4 6.55 6.55 6.55 9.53 9.53 9.53 12.7 15.88 19.05
150 168.3 2.77 2.77 3.4 3.4 7.11 7.11 7.11 10.97 10.97 10.97 14.27 18.26 21.95
200 219.1 2.77 2.77 3.76 3.76 6.35 7.04 8.18 8.18 8.18 10.31 12.7 12.7 12.7 15.09 18.26 20.62 23.01 22.23
250 273 3.4 3.4 4.19 4.19 6.35 7.8 9.27 9.27 9.27 12.7 15.09 12.7 12.7 18.26 21.44 25.4 28.58 25.4
300 323.8 3.96 3.96 4.57 4.57 6.35 8.38 10.31 9.53 9.53 14.27 17.48 12.7 12.7 21.44 25.4 28.58 33.32 25.4
350 355.6 3.96 3.96 6.35 4.78 7.92 9.53 11.13 9.53 9.53 15.09 19.05 12.7 12.7 23.83 27.79 31.75 35.71
400 406.4 4.19 4.19 6.35 4.78 7.92 9.53 12.7 9.53 9.53 16.66 21.44 12.7 12.7 26.19 30.96 36.53 40.49
450 457 4.19 4.19 6.35 4.78 7.92 11.13 14.27 9.53 9.53 19.05 23.83 12.7 12.7 29.36 34.93 39.67 45.24
500 508 4.78 4.78 6.35 5.54 9.53 12.7 15.09 9.53 9.53 20.62 26.19 12.7 12.7 32.54 38.1 44.45 50.01
550 559 4.78 4.78 6.35 5.54 9.53 12.7 9.53 22.23 28.58 12.7 34.93 41.28 47.63 53.98
600 610 5.54 5.54 6.35 6.35 9.53 14.27 17.48 9.53 9.53 24.61 30.96 12.7 12.7 38.89 46.02 52.37 59.54
650 660 7.92 12.7 9.53 12.7
700 711 7.92 12.7 15.88 9.53 12.7
750 762 6.35 6.35 7.92 7.92 12.7 15.88 9.53 12.7
800 813 7.92 12.7 15.88 17.48 9.53 12.7
850 864 7.92 12.7 15.88 17.48 9.53 12.7
900 914 7.92 12.7 15.88 19.05 9.53 12.7
950 965 9.53 12.7
1000 1016 9.53 12.7
1050 1067 9.53 12.7
1100 1118 9.53 12.7
1150 1168 9.53 12.7
1200 1219 9.53 12.7
DN in mm OD 5 5s 10 10s 20 30 40 40s Std 60 80 80s XS 100 120 140 160 XXS DN in mm
ASME B36.10M-2015: Welded and Seamless Wrought Steel Pipe
ASME B36.19M-2004: Stainless Steel Pipe (For 5S,10S,40S and 80S)

Nominal Pipe Size OD

Nominal Pipe Size
in Inch
Nominal Pipe Size
OD in Inch
DN in mm Nominal Pipe Size
OD in mm
1/8 10.3 6 10.3
1/4 13.7 8 13.7
3/8 17.1 10 17.1
1/2 21.3 15 21.3
3/4 26.7 20 26.7
1 33.4 25 33.4
1.25 42.2 32 42.2
1.5 48.3 40 48.3
2 60.3 50 60.3
2.5 73 65 73
3 88.9 80 88.9
3.5 101.6 90 101.6
4 114.3 100 114.3
5 141.3 125 141.3
6 168.3 150 168.3
8 219.1 200 219.1
10 273.1 250 273.1
12 323.8 300 323.8
14 14 350 355.6
16 16 400 406.4
18 18 450 457
20 20 500 508
22 22 550 559
24 24 600 610
26 26 650 660
28 28 700 711
30 30 750 762
32 32 800 813
34 34 850 864
36 36 900 914
38 38 950 965
40 40 1000 1016
42 42 1050 1067
44 44 1100 1118
46 46 1150 1168
48 48 1200 1219

You can calculate Pipe Inside Diameter (ID) with the help of Outside Diameter (OD) and Thickness of the pipe by using formula given below.

Pipe ID = [Pipe O.D. – (2×Pipe wall thickness)]

Dimension Tolerance for Carbon Steel and Stainless Steel Pipe

Common dimension tolerances are listed in ASTM A530. However, each product has its own requirements and when given in that specification that will govern over the A530.

Description Size Over Under
Weight NPS 12 (DN 300) and under 10% 3.50%
Weight NPS 14 (DN 350) and above (Note-1) 10% 5%
Wall Thickness
Seamless and Welded Pipe 1⁄8 to 2 ½, incl., all t/D ratios (Note-2) 20.00% 12.50%
3 to 18 incl., t/D up to 5 % incl. 22.50% 12.50%
3 to 18 incl., t/D > 5 % 15.00% 12.50%
20 and larger, welded, all t/D ratios (Note-3) 17.50% 12.50%
20 and larger, seamless, t/D up to 5 % incl. 22.50% 12.50%
20 and larger, seamless, t/D > 5 % 15.00% 12.50%
Forged and Bored Pipe 1/8 in.(3.2mm) Nil
Cast Pipe 1/6 in.(1.6mm) Nil
Inside Diameter for Cast Pipe Nil 1⁄16 in. (1.6 mm)
Outside Diameter (Note-4)
DiameterOutside 1⁄8 to 11⁄2, incl 1⁄64 in. (0.4mm) 1/32 in. (0.8mm)
Over 1 ½ to 4, incl 1/32 in. (0.8mm) 1/32 in. (0.8mm)
Over 4 to 8, inc 1/16 in. (1.6mm) 1/32 in. (0.8mm)
Over 8 to 18, incl 3/32 in. (2.4mm) 1/32 in. (0.8mm)
Over 18 to 26, incl 1/8 in. (3.2mm) 1/32 in. (0.8mm)
Over 26 to 34, incl 5/32 in. (4.0mm) 1/32 in. (0.8mm)
Over 34 3/8 in. (4.8mm) 1/32 in. (0.8mm)
As per ASTM A530/A530M-12 and ASTM A999/A999M-15
  • Note-1: Pipe of NPS 4 (DN 100) and smaller may be weighed in lots; pipe in sizes larger than NPS 4 (DN 100) shall be weighed separately.
  • Note-2: t = Nominal wall thickness. D = Outside diameter.
  • Note-3: For welded pipe, the weld area shall not be limited by the over tolerance.
  • Note-4: For thin-wall pipe, the ovality in any one cross-section shall not exceed 1.5 % of the specified outside diameter.

Click on the Below Image to get your Printable Pipe Size Chart

Pocket Chart in Inches

nominal pipe size chart In mm

Pocket Chart in MM

nominal pipe size chart In mm

Download PDF Charts for Free

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