Stainless Steel Pipe Size Chart: OD, Wall Thickness & Schedule

If you only need a number, here is the short version. Stainless steel pipe is sized by nominal pipe size, or NPS, and schedule under ASME B36.19M. The outside diameter is fixed for each NPS, and the schedule sets the wall. Aashish Metals supplies stainless pipe across these sizes, and this chart is built to the same ASME B36.19M figures our team checks orders against.

 The stainless steel pipe size chart below gives NPS, DN, OD in mm and inches, and wall thickness for 5S, 10S, 40S and 80S, so it works as a quick stainless steel pipe dimensions chart. Every figure is checked against ASME B36.19M. Go straight to Table A, or read on to see how to use it. For the wider picture, see our steel pipe types, sizes and buying guide.

SS Pipe Size Chart in mm and Inches, From NPS One Eighth to 24

Table A. SS pipe size chart with NPS to DN conversion, OD and wall thickness in mm

Source, ASME B36.19M. NA means that schedule does not exist at that size. Fractional sizes are written out, so one half means the half inch size.

Read across a row. The OD does not change from one schedule to the next, only the wall does. A heavier schedule therefore means a smaller bore for the same outside size, which matters for flow and for fit inside flanges and fittings. The 5S schedule begins at NPS one half. NPS 22 exists in ASME B36.19M but is rarely used, so it is left out. Treat every wall value as nominal when you use this stainless steel pipe size chart for ordering.

Note on 160S and XXS. Schedules 160S and XXS are not part of ASME B36.19M. Heavier walls such as Sch 160 and XXS come from ASME B36.10M and are used with stainless steel only when a project specification calls for them.

How to Read Stainless Steel Pipe OD and Wall Thickness

Before using any stainless steel pipe size chart, it helps to be clear on six terms.

• NPS. Nominal pipe size in inches. It is a name for the size and not a measurement.
• DN. The metric label for the same size, such as DN 50 for NPS 2.
• OD. Outside diameter, fixed for each NPS.
• Wall thickness. The thickness of the pipe wall, set by the schedule.
• ID. Inside diameter, which equals the OD minus twice the wall.
• Schedule. The code, such as 10S, that picks the wall for a given NPS.

Worked example. Take 2 in NPS in 10S. The OD is 60.3 mm and the wall is 2.77 mm. The ID is 60.3 minus 2 times 2.77, which gives 54.76 mm.

Why NPS is a name and not a measurement. For NPS 12 and under, the real OD is larger than the number. NPS 2 has an OD of 2.375 in, or 60.3 mm, and NPS 12 has an OD of 12.75 in. From NPS 14 upward the OD in inches matches the NPS number.

ASME B36.19M Pipe Sizes vs B36.10M, Why Stainless Schedules Differ

ASME B36.19M covers stainless steel pipe. ASME B36.10M covers carbon and alloy steel pipe. The two overlap at small sizes and then part ways, which is why a stainless Sch 40 row can differ from a carbon steel one.

The rule is short. 40S equals Sch 40 up to NPS 10. 80S equals Sch 80 only up to NPS 8. At NPS 10, 80S is 12.70 mm while Sch 80 is 15.09 mm. At NPS 12, 40S is 9.53 mm while Sch 40 is 10.31 mm.

Table B. Where B36.19M stainless and B36.10M carbon and alloy schedules differ, wall in mm

Source, ASME B36.19M and ASME B36.10M.

Stainless S series walls stop at 9.53 mm for 40S and 12.70 mm for 80S at large sizes. Do not assume a carbon steel schedule table applies to stainless above NPS 8. For the 40S and Sch 40 comparison at a single size, see our page on Schedule 40 steel pipe. For the numbered schedules, read the pipe schedule chart explained guide and the pipe schedule and thickness tables.

Stainless Steel Pipe ID and Weight per Metre

Once you have the wall, the next questions are usually the ID and the weight. ID equals OD minus twice the wall. Weight in kg per metre equals OD minus wall, multiplied by wall, multiplied by 0.02491, with both values in mm. The factor is for SS 304 at a density of 7.93 grams per cubic centimetre, and you can check other metals in our metal density chart. Grade 316 and 316L run about 1 to 2 percent heavier, and actual mill weight varies with the thickness tolerance.

Table C. Wall, ID and weight per metre for 10S, 40S and 80S

Pipe vs Tube, Why the Sizing Rules Differ

People often use the two words as if they were one. They are sized differently.

If your line is tube and not pipe, size it by actual OD and wall. See our guide to instrumentation tube fittings for that side of the work.

Tolerances, Standards and Grades That Use This Chart

• ASTM A312. Seamless and welded austenitic pipe. Minimum wall is 12.5 percent below nominal.
• ASTM A358. Electric fusion welded pipe, mostly large bore.
• ASTM A790. Duplex pipe. Duplex may be supplied in thinner walls because of its higher strength, so read our note on duplex stainless steel grades.

Grades covered include 304 and 304L, 316 and 316L, 321, 347, 310S, 904L and duplex. The dimensions are the same across the austenitic grades and only the weight changes slightly, which is the point of the SS 304 vs SS 316 differences guide. That is why one stainless steel pipe size chart serves them all.

How to Choose the Right Schedule

• Pressure and temperature. Start from the design pressure and the metal temperature, and check the allowable stress for the grade.
• Corrosion allowance. Add wall if the service will thin the pipe over its life.
• Welding and threading. Threading needs 40S or thicker, because the thread cuts into the wall.
• Flange and fitting match. Make sure the bore and wall suit the fittings you will weld to.
• Weight and cost. A lighter schedule saves material, but only where the first four points allow it.

Confirm the final choice against the project specification.