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
2.37560.30.1543.912.06752.5
For NPS 14 Schedule 40 pipe
143500.43811.1313.124333.3

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
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 SizeDiameter NominalNominal Pipe SizeDiameter Nominal
NPS (inches)DN (mm)NPS (inches)DN (mm)
1/8620500
1/4822550
3/81024600
1/21526650
3/42028700
12530750
1 ¼3232800
1 ½4036900
250401000
2 ½65421050
380441100
3 ½90481200
4100521300
5125561400
6150601500
8200641600
10250681700
12300721800
14350761900
16400802000
18450Based 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.

Piping Courses

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 B36.105, 10, 20, 30, 40, 60, 80, 100, 120, 140, 160, STD, XS, XXS
For Stainless Steel Pipe as per ASME B36.195S, 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 InchOD55s1010s20304040sStd608080sXS100120140160XXSSize in Inch
1/80.4050.0490.0490.0680.0680.0680.0950.0950.0951/8
1/40.540.0650.0650.0880.0880.0880.1190.1190.1191/4
3/80.6750.0650.0650.0730.0910.0910.0910.1260.1260.1263/8
1/20.840.0650.0650.0830.0830.0950.1090.1090.1090.1470.1470.1470.1880.2941/2
3/41.050.0650.0650.0830.0830.0950.1130.1130.1130.1540.1540.1540.2190.3083/4
11.3150.0650.0650.1090.1090.1140.1330.1330.1330.1790.1790.1790.250.3581
1 1/41.660.0650.0650.1090.1090.1170.140.140.140.1910.1910.1910.250.3821 1/4
1 1/21.90.0650.0650.1090.1090.1250.1450.1450.1450.20.20.20.2810.41 1/2
22.3750.0650.0650.1090.1090.1250.1540.1540.1540.2180.2180.2180.3440.4362
2 1/22.8750.0830.0830.120.120.1880.2030.2030.2030.2760.2760.2760.3750.5522 1/2
33.50.0830.0830.120.120.1880.2160.2160.2160.30.30.30.4380.63
3 1/240.0830.0830.120.120.1880.2260.2260.2260.3180.3180.3180.6363 1/2
44.50.0830.0830.120.120.1880.2370.2370.2370.3370.3370.3370.4380.5310.6744
55.5630.1090.1090.1340.1340.2580.2580.2580.3750.3750.3750.50.6250.755
66.6250.1090.1090.1340.1340.280.280.280.4320.4320.4320.5620.7190.8646
88.6250.1090.1090.1480.1480.250.2770.3220.3220.3220.4060.50.50.50.5940.7190.8120.9060.8758
1010.750.1340.1340.1650.1650.250.3070.3650.3650.3650.50.5940.50.50.7190.84411.125110
1212.750.1560.1560.180.180.250.330.4060.3750.3750.5620.6880.50.50.84411.1251.312112
14140.1560.1560.250.1880.3120.3750.4380.3750.3750.5940.750.50.50.9381.0941.251.40614
16160.1650.1650.250.1880.3120.3750.50.3750.3750.6560.8440.50.51.0311.2191.4381.59416
18180.1650.1650.250.1880.3120.4380.5620.3750.3750.750.9380.50.51.1561.3751.5621.78118
20200.1880.1880.250.2180.3750.50.5940.3750.3750.8121.0310.50.51.2811.51.751.96920
22220.1880.1880.250.2180.3750.50.3750.8751.1250.51.3751.6251.8752.12522
24240.2180.2180.250.250.3750.5620.6880.3750.3750.9691.2190.50.51.5311.8122.0622.34424
26260.3120.50.3750.5
28280.3120.50.6250.3750.5
30300.250.250.3120.3120.50.6250.3750.5
32320.3120.50.6250.6880.3750.5
34340.3120.50.6250.6880.3750.5
36360.3120.50.6250.750.3750.5
38380.3750.5
40400.3750.5
42420.3750.5
44440.3750.5
46460.3750.5
48480.3750.5
Size in InchOD55s1010s20304040sStd608080sXS100120140160XXSSize 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 mmOD55s1010s20304040sStd608080sXS100120140160XXSDN in mm
610.31.241.241.731.731.732.412.412.41
813.71.651.652.242.242.243.023.023.02
1017.11.651.651.852.312.312.313.23.23.2
1521.31.651.652.112.112.412.772.772.773.733.733.734.787.47
2026.71.651.652.112.112.412.872.872.873.913.913.915.567.82
2533.41.651.652.772.772.93.383.383.384.554.554.556.359.09
3242.21.651.652.772.772.973.563.563.564.854.854.856.359.7
4048.31.651.652.772.773.183.683.683.685.085.085.087.1410.16
5060.31.651.652.772.773.183.913.913.915.545.545.548.7411.07
65732.112.113.053.054.785.165.165.167.017.017.019.5314.02
8088.92.112.113.053.054.785.495.495.497.627.627.6211.1315.24
90101.62.112.113.053.054.785.745.745.748.088.088.0816.15
100114.32.112.113.053.054.786.026.026.028.568.568.5611.1313.4917.12
125141.32.772.773.43.46.556.556.559.539.539.5312.715.8819.05
150168.32.772.773.43.47.117.117.1110.9710.9710.9714.2718.2621.95
200219.12.772.773.763.766.357.048.188.188.1810.3112.712.712.715.0918.2620.6223.0122.23
2502733.43.44.194.196.357.89.279.279.2712.715.0912.712.718.2621.4425.428.5825.4
300323.83.963.964.574.576.358.3810.319.539.5314.2717.4812.712.721.4425.428.5833.3225.4
350355.63.963.966.354.787.929.5311.139.539.5315.0919.0512.712.723.8327.7931.7535.71
400406.44.194.196.354.787.929.5312.79.539.5316.6621.4412.712.726.1930.9636.5340.49
4504574.194.196.354.787.9211.1314.279.539.5319.0523.8312.712.729.3634.9339.6745.24
5005084.784.786.355.549.5312.715.099.539.5320.6226.1912.712.732.5438.144.4550.01
5505594.784.786.355.549.5312.79.5322.2328.5812.734.9341.2847.6353.98
6006105.545.546.356.359.5314.2717.489.539.5324.6130.9612.712.738.8946.0252.3759.54
6506607.9212.79.5312.7
7007117.9212.715.889.5312.7
7507626.356.357.927.9212.715.889.5312.7
8008137.9212.715.8817.489.5312.7
8508647.9212.715.8817.489.5312.7
9009147.9212.715.8819.059.5312.7
9509659.5312.7
100010169.5312.7
105010679.5312.7
110011189.5312.7
115011689.5312.7
120012199.5312.7
DN in mmOD55s1010s20304040sStd608080sXS100120140160XXSDN 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 mmNominal Pipe Size
OD in mm
1/810.3610.3
1/413.7813.7
3/817.11017.1
1/221.31521.3
3/426.72026.7
133.42533.4
1.2542.23242.2
1.548.34048.3
260.35060.3
2.5736573
388.98088.9
3.5101.690101.6
4114.3100114.3
5141.3125141.3
6168.3150168.3
8219.1200219.1
10273.1250273.1
12323.8300323.8
1414350355.6
1616400406.4
1818450457
2020500508
2222550559
2424600610
2626650660
2828700711
3030750762
3232800813
3434850864
3636900914
3838950965
404010001016
424210501067
444411001118
464611501168
484812001219

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.

DescriptionSizeOverUnder
WeightNPS 12 (DN 300) and under10%3.50%
WeightNPS 14 (DN 350) and above (Note-1)10%5%
Wall Thickness
Seamless and Welded Pipe1⁄8 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 Pipe1/8 in.(3.2mm)Nil
Cast Pipe1/6 in.(1.6mm)Nil
Inside Diameter for Cast PipeNil1⁄16 in. (1.6 mm)
Outside Diameter (Note-4)
DiameterOutside1⁄8 to 11⁄2, incl1⁄64 in. (0.4mm)1/32 in. (0.8mm)
Over 1 ½ to 4, incl1/32 in. (0.8mm)1/32 in. (0.8mm)
Over 4 to 8, inc1/16 in. (1.6mm)1/32 in. (0.8mm)
Over 8 to 18, incl3/32 in. (2.4mm)1/32 in. (0.8mm)
Over 18 to 26, incl1/8 in. (3.2mm)1/32 in. (0.8mm)
Over 26 to 34, incl5/32 in. (4.0mm)1/32 in. (0.8mm)
Over 343/8 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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