Steel Pipe Sizes and Dimensions Chart: NPS, DN, OD, Wall Thickness and Weight

Steel pipe sizing becomes straightforward once you understand one rule: the nominal pipe size is a designation, not a direct measurement of the pipe’s outside or inside diameter. For example, an NPS 2 pipe has an actual outside diameter of 2.375 inches rather than 2 inches.

This steel pipe sizes and dimensions chart brings together NPS, DN, outside diameter, pipe schedule, wall thickness, inside diameter and theoretical weight. Use the pipe size chart to identify standard dimensions, then confirm the material specification, manufacturing tolerance and design requirements before ordering.

Steel Pipe Sizes and Dimensions Chart

The following pipe sizing chart lists standard NPS designations, corresponding DN values and actual outside diameters. These dimensions apply to steel pipe manufactured to the ASME B36.10 dimensional system.

For NPS 12 and smaller, the actual outside diameter is numerically larger than the nominal size. From NPS 14 upward, the NPS number generally matches the actual outside diameter in inches.

NPS	DN	Outside Diameter, in	Outside Diameter, mm
1/8	6	0.405	10.3
1/4	8	0.540	13.7
3/8	10	0.675	17.1
1/2	15	0.840	21.3
3/4	20	1.050	26.7
1	25	1.315	33.4
1 1/4	32	1.660	42.2
1 1/2	40	1.900	48.3
2	50	2.375	60.3
2 1/2	65	2.875	73.0
3	80	3.500	88.9
3 1/2	90	4.000	101.6
4	100	4.500	114.3
5	125	5.563	141.3
6	150	6.625	168.3
8	200	8.625	219.1
10	250	10.750	273.0
12	300	12.750	323.8
14	350	14.000	355.6
16	400	16.000	406.4
18	450	18.000	457.2
20	500	20.000	508.0
22	550	22.000	558.8
24	600	24.000	609.6

Reading the Pipe Dimensions Chart

Start with the NPS or DN specified on the drawing. Then confirm the actual OD before choosing fittings, flanges, clamps or fabrication equipment.

For example, a drawing that specifies DN 80 corresponds to:

NPS 3
3.500-inch outside diameter
88.9 mm outside diameter

Do not convert DN 80 into inches by dividing 80 by 25.4. DN and NPS are standardized designations rather than direct physical measurements.

Pipe Schedule Chart and Pipe Wall Thickness Chart

A pipe schedule identifies a standardized wall-thickness series. It is not a wall-thickness measurement and does not represent a single pressure rating.

The same schedule has different wall thicknesses at different NPS values. For example, Schedule 40 has a nominal wall thickness of 0.133 inch for NPS 1 but 0.365 inch for NPS 10.

The following pipe schedule chart shows common nominal wall thicknesses in inches.

NPS	OD, in	Sch 5	Sch 10	Sch 40	Sch 80	Sch 160
1/2	0.840	0.065	0.083	0.109	0.147	0.187
3/4	1.050	0.065	0.083	0.113	0.154	0.218
1	1.315	0.065	0.109	0.133	0.179	0.250
1 1/4	1.660	0.065	0.109	0.140	0.191	0.250
1 1/2	1.900	0.065	0.109	0.145	0.200	0.281
2	2.375	0.065	0.109	0.154	0.218	0.343
2 1/2	2.875	0.083	0.120	0.203	0.276	0.375
3	3.500	0.083	0.120	0.216	0.300	0.437
4	4.500	0.083	0.120	0.237	0.337	0.531
5	5.563	0.109	0.134	0.258	0.375	0.625
6	6.625	0.109	0.134	0.280	0.432	0.719
8	8.625	0.109	0.148	0.322	0.500	0.906
10	10.750	0.134	0.165	0.365	0.594	1.125
12	12.750	0.156	0.180	0.406	0.688	1.312

These are nominal dimensions. The actual delivered wall thickness may vary within the tolerances permitted by the applicable material and manufacturing specification.

Schedule 40 and Schedule 80 Wall Thickness

Schedule 40 and Schedule 80 pipes with the same NPS normally share the same outside diameter. Schedule 80 has a thicker wall, so it has a smaller inside diameter and a higher theoretical weight.

NPS	Sch 40 Wall, in	Sch 40 Wall, mm	Sch 80 Wall, in	Sch 80 Wall, mm
1/2	0.109	2.77	0.147	3.73
3/4	0.113	2.87	0.154	3.91
1	0.133	3.38	0.179	4.55
1 1/4	0.140	3.56	0.191	4.85
1 1/2	0.145	3.68	0.200	5.08
2	0.154	3.91	0.218	5.54
2 1/2	0.203	5.16	0.276	7.01
3	0.216	5.49	0.300	7.62
3 1/2	0.226	5.74	0.318	8.08
4	0.237	6.02	0.337	8.56
5	0.258	6.55	0.375	9.53
6	0.280	7.11	0.432	10.97
8	0.322	8.18	0.500	12.70
10	0.365	9.27	0.594	15.09
12	0.406	10.31	0.688	17.48

For a more focused comparison, see the BAOLAI guide to Schedule 80 pipe thickness and dimensions.

STD, XS and XXS Wall Designations

Older drawings and purchase specifications may use STD, XS or XXS instead of schedule numbers.

STD means Standard Weight.
XS means Extra Strong.
XXS means Double Extra Strong.

STD has the same nominal wall thickness as Schedule 40 through NPS 10. From NPS 12 upward, the two designations are no longer equivalent.

XS generally matches Schedule 80 through NPS 8. Above that size, XS commonly remains at a 0.500-inch nominal wall while Schedule 80 becomes progressively thicker.

XXS should not automatically be treated as Schedule 160. The two designations have different wall thicknesses at several pipe sizes.

Nominal Pipe Size Chart: NPS, DN and Outside Diameter

Nominal pipe size is the North American designation used to identify standard pipe sizes. An NPS number does not directly state the measured OD or ID.

The nominal pipe size chart near the beginning of this guide connects three different values:

NPS, the North American nominal designation
DN, the corresponding international nominal designation
OD, the actual outside diameter

Nominal Pipe Size Is Not an Actual Diameter

For NPS 1/8 through NPS 12, the NPS number is smaller than the actual OD. An NPS 2 pipe, for example, has an OD of 2.375 inches.

This system allows pipes of the same NPS but different schedules to connect to compatible fittings. The OD remains fixed while the wall thickness extends inward and changes the ID.

Reading an NPS Pipe Chart

To use an NPS pipe chart correctly:

Locate the specified NPS.
Confirm its corresponding DN.
Read the actual outside diameter.
Select the required pipe schedule.
Use the schedule to find the wall thickness.
Calculate or verify the inside diameter and weight.

An NPS pipe must therefore be ordered with more information than the nominal size alone. A complete purchase description should include the size, schedule or wall thickness, material specification, grade, manufacturing process, length and end finish.

Using an NPS Pipe Size Chart in Procurement

Suppose a bill of materials specifies NPS 6 Schedule 80 pipe.

The NPS pipe size chart shows:

NPS: 6
DN: 150
Actual OD: 6.625 inches or 168.3 mm
Nominal wall thickness: 0.432 inch or 10.97 mm
Calculated ID: approximately 5.761 inches or 146.3 mm

These dimensions should be checked against the fittings, pressure design, corrosion allowance and dimensional tolerances required by the project.

What Is DN in Pipe Sizing?

DN means nominal diameter. ISO 6708 defines DN as the nominal-size designation applied to components in a piping system.

Pipe DN values do not represent exact measured diameters in millimetres. For example, DN 50 corresponds to NPS 2, but an NPS 2 steel pipe has an actual OD of 60.3 mm.

DN Pipe Size Chart and DN to Inch Conversion

A DN pipe size chart should be used as a standardized cross-reference rather than a mathematical conversion table.

DN	NPS	Nominal Inch Designation	Actual OD, mm
6	1/8	1/8 inch	10.3
8	1/4	1/4 inch	13.7
10	3/8	3/8 inch	17.1
15	1/2	1/2 inch	21.3
20	3/4	3/4 inch	26.7
25	1	1 inch	33.4
32	1 1/4	1 1/4 inch	42.2
40	1 1/2	1 1/2 inch	48.3
50	2	2 inch	60.3
65	2 1/2	2 1/2 inch	73.0
80	3	3 inch	88.9
100	4	4 inch	114.3
150	6	6 inch	168.3
200	8	8 inch	219.1
250	10	10 inch	273.0
300	12	12 inch	323.8

For a DN to inch conversion, match the DN designation to its corresponding NPS. Do not divide the DN number by 25.4 because DN pipe sizes are nominal rather than physical measurements.

Pipe OD Chart: Outside Diameter and Inside Diameter

The pipe OD chart shows that each NPS has a standardized outside diameter. That OD normally remains unchanged across the available schedules for that NPS.

The inside diameter is different because it depends on wall thickness:

Inside Diameter = Outside Diameter − 2 × Wall Thickness

For an NPS 4 pipe:

Schedule	Outside Diameter, in	Wall Thickness, in	Calculated Inside Diameter, in
Schedule 10	4.500	0.120	4.260
Schedule 40	4.500	0.237	4.026
Schedule 80	4.500	0.337	3.826
Schedule 160	4.500	0.531	3.438

The OD stays at 4.500 inches, while the bore becomes smaller as the schedule increases.

Outside Diameter Controls Component Fit

OD is critical when selecting:

Flanges
Grooved couplings
Clamps and supports
Gaskets
Rollers and bending equipment
Coating and insulation systems

Using the nominal size as if it were the actual OD can result in incompatible components and failed incoming inspection.

Inside Diameter Affects Flow and Fit-Up

ID affects the available flow area and the ability to insert another component into the pipe. It may also influence pressure loss, cleaning access and internal lining requirements.

When a project has a minimum-bore requirement, specify the required ID or minimum wall condition instead of relying only on NPS and schedule.

Steel Pipe Weight Chart and Calculation

Pipe weight increases with both OD and wall thickness. Schedule 80 pipe is therefore heavier than Schedule 40 pipe of the same NPS.

The following values are approximate theoretical weights for common carbon steel pipe sizes.

NPS	Sch 40, lb/ft	Sch 40, kg/m	Sch 80, lb/ft	Sch 80, kg/m
1/2	0.85	1.27	1.09	1.62
1	1.68	2.50	2.17	3.23
2	3.65	5.43	5.02	7.47
3	7.58	11.28	10.25	15.25
4	10.79	16.06	14.98	22.29
6	18.97	28.23	28.57	42.51
8	28.55	42.49	43.39	64.57
10	40.48	60.24	64.43	95.87
12	49.56	73.76	88.63	131.91

Actual shipment weight can differ because of dimensional tolerances, steel density, coatings and manufacturing variation.

Calculating Steel Pipe Weight

For carbon steel pipe, theoretical weight can be estimated with the following formulas.

When D and t are measured in inches:

Weight in lb/ft = 10.69 × (D − t) × t

When D and t are measured in millimetres:

Weight in kg/m = 0.02466 × (D − t) × t

In both formulas:

D is the actual outside diameter.
t is the nominal wall thickness.

For example, an NPS 4 Schedule 40 pipe has an OD of 4.500 inches and a nominal wall thickness of 0.237 inch:

Weight = 10.69 × (4.500 − 0.237) × 0.237
Weight ≈ 10.79 lb/ft

For bundle, lifting and freight calculations, multiply the weight per unit length by the actual ordered length and quantity. The complete process is explained in BAOLAI’s steel pipe weight calculation guide.

ASME Standards for Steel Pipe Dimensions

Pipe dimensions and material specifications perform different functions. A dimensional standard defines the OD and nominal wall thickness series, while a material specification defines matters such as chemical composition, mechanical properties, manufacturing method and testing.

ASME B36.10 Defines Wrought Steel Pipe Dimensions

ASME B36.10 standardizes dimensions for welded and seamless wrought steel pipe used under high- or low-temperature and pressure conditions. It provides the NPS, OD, schedule and nominal wall-thickness system used throughout this article.

The standard applies the term “pipe” to tubular products manufactured in dimensions commonly used for pipeline and piping systems. This distinguishes pipe from tube, which is generally ordered by an actual outside dimension and wall thickness.

ASME B36.19 Defines Stainless Steel Pipe Dimensions

ASME B36.19 covers welded and seamless wrought stainless steel pipe. Its schedules use an “S” suffix, including Schedule 5S, 10S, 40S and 80S.

Do not assume that an “S” schedule always has the same wall thickness as the same number without the suffix. ASME notes specific differences between B36.19 and B36.10, including certain Schedule 10S, 40S and 80S sizes.

ASTM Specifications Define Material Requirements

ASTM A53, A106 and A312 are material and product specifications rather than general pipe schedule charts.

For example:

ASTM A53 covers black and hot-dip galvanized welded and seamless steel pipe for specified applications.
ASTM A106 covers seamless carbon steel pipe intended for high-temperature service.
ASTM A312 covers seamless, welded and heavily cold-worked austenitic stainless steel pipe.

A pipe can therefore be described as ASTM A106 Grade B, NPS 6, Schedule 80. Each part of that description provides different information.

BAOLAI supplies carbon seamless steel pipes in multiple ASTM and API specifications for industrial projects.

How to Select the Right Steel Pipe Size and Schedule

A pipe size chart is a dimensional reference, not a complete design method. The final size and wall thickness must match the operating conditions and applicable engineering code.

Confirming the Required OD and ID

Start with the connection and flow requirements.

Confirm the OD when matching the pipe with fittings, flanges, supports or processing equipment. Confirm the ID when the project has minimum-flow, minimum-bore, insertion or internal-cleaning requirements.

Calculating the Minimum Required Wall Thickness

The required wall depends on more than the design pressure. Engineering calculations may also need to account for:

Steel grade and allowable stress
Design temperature
Corrosion or erosion allowance
Weld-joint quality factor
Manufacturing tolerance
Bending and forming allowance
External pressure or vacuum
Mechanical loads and vibration

After calculating the minimum required wall, select the next suitable standard schedule. BAOLAI’s guide to selecting steel pipe wall thickness explains this process in more detail.

Checking the Material Specification

The same NPS and schedule can be available under different ASTM, API or EN specifications. These pipes may share dimensional values but differ in chemistry, strength, heat treatment, inspection and intended service.

Do not select a pipe solely because its dimensions match the drawing.

Confirming Manufacturing Tolerances

The dimensions in a pipe dimensions chart are nominal values. The applicable material specification may permit variation in:

Outside diameter
Wall thickness
Length
Straightness
End preparation
Theoretical or actual weight

When fit-up or minimum wall is critical, state the required tolerances in the purchase order and inspection plan.

Common Steel Pipe Sizing Mistakes

Treating NPS as the Actual Outside Diameter

An NPS 2 pipe has an actual OD of 2.375 inches. Ordering clamps or fittings based on a 2-inch measured OD will result in a mismatch.

Treating DN as a Millimetre Measurement

DN 50 does not mean the pipe has a 50 mm OD. It corresponds to NPS 2, which has a 60.3 mm OD.

Reading a Schedule Number as Wall Thickness

Schedule 40 is not 40 mm, 0.040 inch or any other fixed thickness. Its wall value changes with NPS.

Using Schedule as a Pressure Rating

A higher schedule usually provides a thicker wall for the same NPS, but schedule alone does not establish allowable working pressure. Material strength, temperature, tolerances, corrosion and the governing design code must also be considered.

Confusing Steel Pipe With Steel Tube

A 2-inch tube is commonly specified with an actual 2.000-inch OD. An NPS 2 pipe has a 2.375-inch OD. Pipe and tube fittings should not be assumed to be interchangeable.

Assuming Schedule 40 and 40S Are Always Identical

Carbon steel and stainless steel dimensional standards overlap in many sizes, but not all corresponding schedule values are the same. Keep the “S” suffix when it is required by the specification.

Frequently Asked Questions About Steel Pipe Sizes

Is steel pipe measured by ID or OD?

Steel pipe is designated by NPS and schedule rather than directly by ID or OD. Each NPS has a standardized OD, while the ID changes according to wall thickness. Physical inspection normally verifies the OD and wall thickness.

Is DN 50 the same as a 2-inch pipe?

DN 50 corresponds to NPS 2 in the nominal sizing system. However, the actual outside diameter is 60.3 mm or 2.375 inches, not 50 mm or exactly 2 inches.

What is the difference between NPS and DN?

NPS is the North American nominal pipe size designation, while DN is the corresponding international nominal designation. Neither should be treated as an exact measured diameter.

Does pipe OD change with schedule?

No. For the same NPS, standard schedules normally share the same outside diameter. Increasing the schedule increases the wall thickness and reduces the inside diameter.

Does a higher pipe schedule mean a higher pressure rating?

Not by itself. A thicker wall can support a higher calculated pressure when other conditions remain equal, but the actual allowable pressure depends on material grade, temperature, manufacturing tolerance, corrosion allowance, fittings and the applicable design code.

Source Steel Pipes in Standard and Custom Dimensions

Correct pipe selection requires more than matching a nominal size. Buyers should define the material specification, grade, NPS or OD, schedule or wall thickness, length, end preparation, coating, quantity and inspection requirements.

BAOLAI supplies seamless and welded steel pipe for pipeline, energy, construction, water transmission and industrial applications. Send the project specification or bill of materials through the BAOLAI contact page to confirm available dimensions, grades, testing and delivery requirements.

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