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Technical Reference
IS 1239 Class A, B, C Pipe Thickness Chart
Light, Medium, and Heavy wall thickness in millimetres for every common NB from 15 to 150 — the chart buyers use for Class B GI and MS pipe enquiries.
Under IS 1239, Class A is Light, Class B is Medium, and Class C is Heavy. Wall thickness depends on nominal bore (NB); it is not one fixed millimetre for every size. For the widely searched 25 NB size, Class A is 2.6 mm, Class B is 3.2 mm, and Class C is 4.0 mm.
Indian procurement for MS and GI ERW tubes almost always lands on this three-class system. Buyers search “b class pipe thickness in mm”, “a class pipe thickness in mm”, “c class pipe thickness”, and “class b gi pipe thickness” because the order line needs a millimetre wall, not only the word Medium. This page consolidates the NB 15–150 chart so the thickness sits next to OD in one place.
Use the table for RFQs, BOQ checks, and weight estimates. Pair it with the IS 1239 standard reference for marking and tolerance context, and with the steel pipe weight calculator when you need kg/m for freight. Wholesale pricing for stock MS and GI lines is on the MS pipe price list and GI pipe price list.
Note: Values below are IS 1239 Part 1 ground-truth dimensions for Class A (Light), Class B (Medium), and Class C (Heavy). Always state NB, class or exact wall (mm), material (MS/GI), length, and end finish on the purchase order. Colour-band trade practice is a field aid, not a substitute for mill marking and MTC.
IS 1239 Class A / B / C Wall Thickness Chart (mm)
Columns show NB (mm), OD (mm), and wall thickness for Class A (Light), Class B (Medium), and Class C (Heavy). All wall values are millimetres.
| NB (mm) | OD (mm) | Class A / Light WT (mm) | Class B / Medium WT (mm) | Class C / Heavy WT (mm) |
|---|---|---|---|---|
| 15 | 21.3 | 2.0 | 2.6 | 3.2 |
| 20 | 26.9 | 2.3 | 2.6 | 3.2 |
| 25 | 33.7 | 2.6 | 3.2 | 4.0 |
| 32 | 42.4 | 2.6 | 3.2 | 4.0 |
| 40 | 48.3 | 2.9 | 3.2 | 4.0 |
| 50 | 60.3 | 2.9 | 3.6 | 4.5 |
| 65 | 76.1 | 3.2 | 3.6 | 4.5 |
| 80 | 88.9 | 3.2 | 4.0 | 4.8 |
| 100 | 114.3 | 3.6 | 4.5 | 5.4 |
| 125 | 139.7 | 4.5 | 4.8 | 5.4 |
| 150 | 165.1 | 4.5 | 4.8 | 5.4 |
What is Class B pipe thickness in mm?
Class B (Medium) thickness depends on NB. At 25 NB it is 3.2 mm; at 50 NB it is 3.6 mm; at 80 NB it is 4.0 mm; at 100 NB it is 4.5 mm. There is no single “Class B millimetre” for every size.
That is why GSC queries such as “b class pipe thickness in mm” and “class b gi pipe thickness” need a full chart, not a one-line myth. Class B is the default Medium grade for general water, structural, and many GI plumbing lines because it balances cost, handling toughness, and pressure capacity for everyday site work. When the BOQ only says “B class GI”, the vendor still needs NB and total metres before a firm rate. For galvanised stock, zinc mass and end finish sit beside the wall class—thickness alone does not define the full commercial line item. Cross-check the chart before converting an old “Medium” note into a purchase order.
Which class for home plumbing / borewell / fire line?
Home plumbing commonly uses Class B (Medium). Light Class A suits only low-pressure, protected duty. Borewell column or casing decisions and fire lines usually need Class B or C per design pressure and handling abuse—follow the project specification.
Residential internal water lines and many site temporary lines stay on Medium because installers clamp, thread, and bury the pipe. Light class can dent and thin further at threads. Fire-hydrant and riser packages often call for heavier wall or a named schedule/system standard in the consultant drawing; do not assume Class B is automatic. Borewell duty is different again: water-well steel casing is typically specified under IS 4270 rather than only as “IS 1239 Class C”, while some GI/MS delivery and column pieces on the farm side still use the A/B/C language. Read the drawing legend first. When in doubt, quote the higher class option with the same NB so the buyer can compare kg/m and price. Product family pages for ERW pipes and tubes help map the right stock line.
How are classes marked?
Indian trade practice commonly marks Light / Class A with a yellow band, Medium / Class B with blue, and Heavy / Class C with red. Always confirm NB, wall, and mill marking—paint can be wrong after rework.
Colour bands are a yard and site convention, not a substitute for the permanent mill stencil and the inspection documents. Bundles get mixed when multiple classes share a truck. Incoming inspection should measure a sample OD and wall with a micrometer or vernier, match heat or batch marks to the MTC, and reject mixed classes that lack clear identification. For tender work, write both the class name and the wall in millimetres on the BOQ so a disputed blue band cannot override a measured 3.2 mm requirement. RP Sales quotes IS 1239 class stock with documentation so commercial buyers can lock the wall before dispatch from Kanpur.
Class vs schedule — are they the same?
No. IS 1239 Class A/B/C is not the same system as ASME pipe schedule (Sch 40, Sch 80). Compare actual wall thickness in millimetres. Use the pipe schedule chart for ASME values.
Schedule numbers come from the ASME B36.10M family used heavily in process and imported equipment packages. Class A/B/C language dominates Indian MS/GI ERW tube trade for water, structural, and general utility pipe. A drawing that says “Sch 40” and a yard that stocks “B class” are not automatically interchangeable even when walls look close at one NB. Always convert both to OD and wall in mm, then to kg/m if freight or support design depends on mass. Mixing the two vocabularies without a conversion step is a common cause of wrong wall on site and failed hydro or fit-up checks.
Frequently Asked Questions
Related Resources
- IS 1239 Standard — Full Reference
- Pipe Schedule Chart (ASME)
- MS Pipe Price List
- GI Pipe Price List
- Steel Pipe Weight Calculator
- ERW Pipes & Tubes
Need IS 1239 Class A / B / C pipe?
Send NB, class or wall (mm), MS or GI, quantity, and delivery PIN — wholesale quotation from Kanpur with documentation.
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