OD (Outside Diameter)
/glossary/odMeasured outside diameter of a pipe or tube, in millimetres or inches, used for fit-up.
Outside diameter is the millimetre you measure across a pipe body before a flange, clamp or coupling is offered. In Kanpur, a 2 inch ASME flange sits on 60.3 mm pipe, not on a 50 mm label. The pipe schedule chart and the IS 1239 class chart both use that 60.3 mm figure. Fit-up checks at Jajmau shops, about 10 km from the yard, start with OD, then wall.
In detail
Outside Diameter (OD) is the measured distance across the external surface of a pipe or tube. Indian water-tube charts list it in millimetres (48.3 mm, 60.3 mm, 114.3 mm). ASME B36.10M lists the same series against NPS and DN. The permissible deviation is taken from the product standard and the ordered size, not from a single commercial plus-or-minus. Put the exact OD on the drawing, then check the delivered pieces under the receiving plan.
What OD is, and what it is not
OD is a physical dimension. A tape, caliper or Pi tape reads it on the pipe body. Indian standards print it in millimetres. American dimensional tables print it in inches and millimetres against NPS.
ASME B36.10M-2018, on the ASME catalogue page, distinguishes pipe from tube. Pipe NPS 12 (DN 300) and smaller have outside diameters numerically larger than the corresponding size. Tube outside diameters are numerically identical to the size number for all sizes. A 50.8 mm boiler tube is a tube OD. A 50 NB water tube is a 60.3 mm pipe OD.
OD is not the bore. Inside diameter is OD minus twice the wall. OD is not a class. Light and Heavy at 50 NB share 60.3 mm and differ by 1.6 mm of wall. OD is not a pressure rating. A schedule number or an IS 1239 class still needs the design calculation.
OD is not a tolerance class. Tolerance class on precision tube is a DIN 2391 / EN 10305 T1 to T4 call-out. Copy that limit from the cylinder drawing. Do not paste a commercial plus-or-minus onto an IS 1239 length.
Who must lock OD, and who can live with an NB label
Lock OD when the piece must enter a flange, a coupling, a clamp, a bored support, or a honed-barrel blank. Panki process shops and Dada Nagar cylinder shops reject a tube that misses the drawing OD even when the NB label looks familiar.
A Kanpur PWD or JJM distribution line can be bought by NB and class because the fittings in that series are built around the same OD. The store still checks OD on receipt when a coupling binds.
Do not order boiler tube by NB. SA192 and SA210 heats on this site are 38.1 mm, 50.8 mm or 63.5 mm OD by a named minimum wall. Do not order IS 3589 trunk pipe by 150 NB; that standard starts at 168.3 mm OD.
A 6 inch note is not one OD. The class chart lists 150 NB at 165.1 mm. The schedule chart lists 6 inch NPS at 168.3 mm. Those two bodies do not share a flange or a coupling without an adapter the drawing did not show.
OD series used on this site
Three dimensional families appear on Kanpur RFQs. The table keeps them apart so a 6 inch note cannot pull the wrong body.
| Family | Size language | Example OD (mm) | Where it is used | Do not mix with |
|---|---|---|---|---|
| IS 1239 Part 1 | NB plus class | 60.3 at 50 NB | Water, gas, fire GI | Sch 40 wall at the same NPS |
| ASME B36.10M | NPS plus schedule | 60.3 at 2 inch | A106 / A53 process pipe | IS 1239 Medium wall 3.6 mm |
| IS 3589 | OD plus wall or class | 168.3 lower bound | JJM / municipal trunks | 150 NB at 165.1 mm |
| Boiler tube | OD times min wall | 50.8 by 3.6 | SA192 / SA210 heats | 50 NB water tube |
| Precision tube | OD times wall or ID | 50.0 by 4.0 | Dada Nagar barrels | IS 1239 class pipe |
IS 3589 also lists 219.1, 273.0, 323.9, 406.4 and 508.0 mm as the DN 200 to DN 500 steps. Those ODs line up with the schedule-chart NPS 8 to 20 rows to within 0.1 mm on DN 250 and DN 300. The wall still comes from the water-pipe design, not from Sch 40 by default.
How to specify OD on an RFQ
Write the millimetre OD even when the BOQ leads with NB or NPS. A missing OD is how the wrong class wall gets offered against a bore the mill never intended for that flange. Send the line on the RFQ.
- OD in millimetres, plus NB or NPS if the drawing uses those labels.
- Wall: IS 1239 class, ASME schedule, or a millimetre thickness. One of those three, not a mix.
- Tolerance: copy the clause from the product standard or the cylinder drawing. Precision tube needs the T-class.
- Ovality and end-diameter limits when the project ITP measures them.
- End finish: plain, bevel, or threaded and coupled. Coupling OD matters on IS 4270 casing.
- Documents: EN 10204 3.1 with the measured OD on the dimensional report when the ITP asks for it.
- Inspection: mill, or named TPI when the PO requires a witnessed diameter check.
- Quantity, length, and delivery basis: ex-warehouse Kanpur or FOR named place.
Worked example: same 60.3 mm OD, Light versus Heavy
Hold OD at 60.3 mm, the 50 NB / 2 inch figure on both site charts. Change only the wall. The pipe-weight table gives Light 2.9 mm at 4.10 kg/m and Heavy 4.5 mm at 6.19 kg/m. Use the site formula once on the Heavy row: W = (OD − t) × t × 0.02466 kg/m.
W = (60.3 − 4.5) × 4.5 × 0.02466 = 55.8 × 4.5 × 0.02466 = 6.19 kg/m. Inside diameter on that Heavy wall is 60.3 − 9.0 = 51.3 mm. Light wall 2.9 mm leaves 54.5 mm ID and 4.10 kg/m on the same table.
One hundred lengths of 6 m are 2,460 kg in Light (24.6 kg each) and 3,710 kg in Heavy (37.1 kg each). The extra 1,250 kg is wall, not a different OD. The MS pipe price list as of 24 May 2026 lists 50 NB Light at ₹50-57 per kg and Heavy at ₹57-65 per kg, both ex-warehouse Kanpur.
A flange bored for 60.3 mm accepts both walls. A flow sheet that used 50 mm as the bore is wrong on both walls. Compute ID from OD and t before a pump curve is signed.
Common OD mistakes on receipt
The first thing that goes wrong is a store measuring once on the coating and rejecting a good body. Zinc on GI adds thickness. Measure steel OD on a cleaned land, or use the mill certificate plus a spot check on a cut end.
A 150 NB coupling is forced onto a 168.3 mm IS 3589 spigot. The class chart and the IS 3589 product manual do not share that diameter. Segregate the pieces and call the designer.
Precision OD is ordered as 50 NB. Dada Nagar barrels are 50.0 mm or 63.0 mm drawn tube, not 60.3 mm class pipe. See DIN 2391 ST52.
Ovality is ignored because the mean OD passed. A clamp or a bored saddle cares about the max reading. Copy the ovality clause from the ordered standard.
A Pi-tape reading is compared with a two-point caliper and both are treated as the same method. Agree the method in the ITP before the truck is booked.
Standards that fix the OD you measure
IS 1239 Part 1:2004 sets the NB-to-OD series used on the class chart, 21.3 mm at 15 NB through 165.1 mm at 150 NB. IS 1239 Part 1 lists 6 to 150 mm NB in the site's BIS preview record; the product manual's stocked series is 15 to 150 mm NB.
IS 3589:2001, titled on the BIS product manual as Steel Pipes for Water and Sewage (168.3 to 2540 mm Outside Diameter), is an OD standard. Construction may be ERW, HFIW, longitudinal SAW or spiral SAW.
ASME B36.10M-2018 is the pipe OD and schedule table behind the site schedule chart. NPS 14 (DN 350) and larger use an OD that equals the inch size: 16 inch is 406.4 mm.
ISO 6708:1995 says any relationship between DN and component dimensions should be given as DN/OD or DN/ID in the product standard. That is why a water isometric writes DN 150 / 168.3 mm OD when it follows the ISO metric series.
Checking OD at the Kanpur yard
Jajmau fabricators, about 10 km east of Bartan Bazar, bring a flange or a clamp drawing and ask for a matching body. The first check on the rack is OD, then wall, then end finish. A 48.3 mm 40 NB piece will not enter a 50 NB socket.
Borewell contractors collecting drill and borewell pipe care about coupling OD as well as body OD. IS 4270 100 mm casing is about 114.3 mm body OD on the site standards page. A binding coupling is an OD problem, not an NB problem.
See steel pipes in Kanpur, seamless pipes in Kanpur, and the Kanpur steel market. Offers are priced ex-warehouse from the Basanti Nagar (208014) yard. Budget GST at 18% extra on the tube line; the tax invoice applies the rate in force.
City pages for Lucknow, Agra, Prayagraj and Varanasi reuse the same OD check at destination. Name the PIN so the e-way bill and the challan carry the same millimetre list.
OD tolerance by product family
IS 1239 and IS 3589 put their own diameter tolerances in the purchased edition. This page does not reprint a plus-or-minus that the public BIS listing does not print. Copy the clause onto the PO.
ASME B36.10M is a dimensional table, not a product specification. Diameter tolerance on A106 or A53 pipe comes from those ASTM documents, not from the schedule chart.
Precision tube uses EN 10305-1 or DIN 2391 T1 to T4. The precision cluster on this site tells buyers to copy the numerical limit from the drawing. A hydraulic H8 bore is an ID class; it does not relax the OD if the barrel is clamped on the outside.
LSAW and HSAW project specs often add ovality and end-diameter limits for field fit-up. Those limits live on the pipeline or water-main specification, not on a stock tag.
Fitment: flanges, couplings and clamps
A weld-neck or slip-on flange is bored for the pipe OD. The 150 lb weld-neck page on this site lists hub and bolt-circle figures against NPS. Matching the NPS without matching the OD series and the ordered wall class is how a bore and a bolt-circle end up on two different bodies.
Threaded IS 1239 couplings follow the same NB-to-OD series as the tube. A T&C 50 NB pair is built around 60.3 mm. Do not thread a 60.3 mm A106 Sch 80 length into that coupling unless the drawing allows mixed standards.
IS 4270 threaded-and-coupled casing uses a separate coupling. The borewell cluster says body OD and coupling OD decide whether the assembly passes the drilled hole; see drill and borewell pipes in Kanpur for that coupling detail.
Structural clamps and saddle supports on a Panki rack are sized to OD. A 88.9 mm 80 NB Medium and an 88.9 mm 3 inch Sch 40 share OD and fight over wall. The clamp cares about the 88.9 mm.
OD versus ID versus the NB label
NB or NPS selects the series. OD is the series number you can measure. ID is derived: ID = OD − 2t. Mass uses OD and t in W = (OD − t) × t × 0.02466, already used above on the 60.3 mm Heavy row.
Flow, velocity and pressure-drop sheets need ID. Fit-up sheets need OD. Weight sheets need OD and t. Putting NB into any of those three sheets is the usual take-off error.
Large-bore transmission and trunk items are best ordered by OD and wall in millimetres rather than by an inch label, since the mill catalogue and the site charts key off that OD number directly. Name the OD on the RFQ line even when the BOQ still carries an NPS or NB column.
When two offers quote the same NB and different ODs, stop the comparison. One offer has left the IS 1239 series. Ask which standard and which table the mill used.
Where you'll meet this in procurement
You will meet OD (Outside Diameter) on size charts, mill quotes, and fitment checks. Cross-check OD (Outside Diameter) against OD, wall thickness or schedule, length, and end finish so the delivered pipe matches flanges, fittings, and pressure duty—not just a familiar nominal label.
Related terms
Related resources
- Pipe schedule chart
- Steel pipe weight calculator
- IS 1239 class thickness chart
- Pipe weight chart
- IS 3589 large-diameter pipe
- Drill and borewell pipes in Kanpur
- Steel pipes in Kanpur
- Seamless steel pipes in Kanpur
- DIN 2391 ST52 tube
- Kanpur steel market
- Request a quotation
- Request a quotation (RFQ)
- Back to full glossary
Key points
- OD is the measured outside diameter. NB is a label. ID is OD minus twice the wall.
- 50 NB and 2 inch NPS share 60.3 mm OD on the site charts. 150 NB is 165.1 mm; 6 inch NPS is 168.3 mm.
- ASME B36.10M-2018: pipe NPS 12 and smaller have OD larger than the size number; tube OD matches the size number.
- Heavy 50 NB at 4.5 mm wall is 6.19 kg/m and 51.3 mm ID. Light at 2.9 mm wall is 4.10 kg/m and 54.5 mm ID.
- Write the millimetre OD on the RFQ even when the BOQ leads with NB or NPS.
Frequently asked questions
Sources
- ASME B36.10M-2018. Welded and Seamless Wrought Steel Pipe: pipe NPS 12 (DN 300) and smaller have OD numerically larger than the size; tube OD matches the size number (American Society of Mechanical Engineers)
- ISO 6708:1995. Pipework components: Definition and selection of DN (nominal size), clause 2.1 and Note 3 (DN/OD or DN/ID) (International Organization for Standardization)
- PM/IS 3589:2001. Product Manual for Steel Pipes for Water and Sewage according to IS 3589:2001 (168.3 to 2540 mm Outside Diameter) (Bureau of Indian Standards)
- PM/1239 (Part 1)/4 Feb 2022. Product Manual for Steel Tubes according to IS 1239 (Part 1):2004: NB 15-150 mm dimensional series (Bureau of Indian Standards)
- IS 1239 : Part 1 : 2004 (reaffirmed 2019). Steel Tubes, Tubulars and Other Wrought Steel Fittings : Part 1 Steel Tubes (Bureau of Indian Standards e-sale (BSB Edge))