Ask ten buyers for "2 inch pipe" and you may get ten different orders. The pipe schedule is what turns a vague size into an exact product. It defines the wall thickness, and with it the weight, pressure rating and price. If your quotations, catalogues and website get the schedule wrong, buyers notice immediately — and many will move on to a supplier who speaks their language.
This guide explains how pipe schedules work, the difference between SCH 10, SCH 40 and SCH 80, and how to present schedules clearly to overseas buyers.
What a pipe schedule actually means
A pipe is described by two numbers: its nominal pipe size (NPS) and its schedule (SCH).
- NPS is a standard size name, not an exact measurement. For NPS 1/8" to 12", the outside diameter (OD) is slightly larger than the nominal size. From NPS 14" upward, the OD equals the nominal size.
- Schedule is a number that sets the wall thickness for that size. A higher schedule means a thicker wall.
The key point: for a given NPS, the outside diameter stays the same across all schedules. Only the wall thickness changes — so the inside diameter gets smaller as the schedule goes up. That is why a 2" SCH 40 and a 2" SCH 80 pipe fit the same fittings and flanges.
Carbon and alloy steel pipe dimensions are covered by ASME B36.10M, and stainless steel pipe by ASME B36.19M (which adds the "S" schedules such as 10S and 40S).
SCH 10 vs SCH 40 vs SCH 80 at a glance
Here are common sizes with their outside diameter and wall thickness in millimetres:
| NPS | OD (mm) | SCH 10 (mm) | SCH 40 (mm) | SCH 80 (mm) |
|---|---|---|---|---|
| 1" | 33.4 | 2.77 | 3.38 | 4.55 |
| 2" | 60.3 | 2.77 | 3.91 | 5.54 |
| 4" | 114.3 | 3.05 | 6.02 | 8.56 |
| 6" | 168.3 | 3.40 | 7.11 | 10.97 |
You can check any size from NPS 1/8" to 24" in our free pipe schedule chart.
SCH 10 — light wall
SCH 10 is thin-walled and light. It is common in stainless steel for low-pressure process lines, food and dairy plants, water systems and fire protection where corrosion resistance matters more than pressure.
SCH 40 — the everyday standard
SCH 40 is the most widely ordered schedule. For sizes up to NPS 10", SCH 40 has the same wall thickness as "STD" (standard weight). It suits general plumbing, water, utilities, structural use and moderate-pressure process piping.
SCH 80 — heavy wall
SCH 80 handles higher pressure and offers more allowance for corrosion and threading. For sizes up to NPS 8", SCH 80 matches "XS" (extra strong). It is popular in oil & gas, steam lines, chemical plants and threaded connections.
How schedule affects weight and price
Because steel is sold by weight, the schedule directly changes the price per metre. For carbon steel, a quick formula is:
Weight (kg/m) = (OD − WT) × WT × 0.02466, with OD and WT in millimetres.
- 2" SCH 40: (60.3 − 3.91) × 3.91 × 0.02466 ≈ 5.44 kg/m
- 2" SCH 80: (60.3 − 5.54) × 5.54 × 0.02466 ≈ 7.48 kg/m
That is almost 40% more steel for the same size. If you quote by the metre but buy by the tonne, getting the schedule wrong can wipe out your margin. Our pipe weight calculator does this instantly for steel, stainless, copper and aluminium.
STD, XS and XXS — the older names
Many buyers still use weight classes instead of schedule numbers:
- STD (standard weight) — same as SCH 40 up to NPS 10".
- XS (extra strong) — same as SCH 80 up to NPS 8".
- XXS (double extra strong) — a very heavy wall with no direct schedule match in most sizes.
Above those sizes the two systems split, so always confirm the actual wall thickness in millimetres or inches when the size is large.
Common mistakes in export enquiries
- Mixing NB and NPS. Indian and European buyers often say "50 NB" or "DN 50" — both refer to the same size as 2" NPS. Show all three on your price list.
- Confusing schedules with IS 1239 classes. Light, Medium and Heavy class MS pipes under IS 1239 are not the same as SCH 10/40/80. Use our IS 1239 pipe chart when a buyer mixes the two.
- Ignoring the "S" in stainless. 10S and 10 are identical in many sizes but not all. Quote exactly what the purchase order says.
- Leaving out the standard. Always state ASME B36.10M or B36.19M along with the material standard, such as ASTM A106 Gr. B or ASTM A312 TP316L.
How to present schedules on your website
International buyers search for exact terms such as "2 inch SCH 80 seamless pipe" or "ASTM A312 SCH 10S". A product page that lists sizes, schedules, OD, wall thickness and weight in a clean table answers their question and ranks better on Google. Add downloadable PDF size charts, and make sure every enquiry form has a field for schedule.
If you want product pages built this way, our export-ready website service is designed for pipe and fitting companies.
Frequently asked questions
Is SCH 40 the same as STD?
For sizes up to NPS 10", yes — SCH 40 and STD have the same wall thickness. From NPS 12" upward they differ, so always confirm the actual wall thickness in millimetres.
Does a higher schedule change the outside diameter?
No. For a given NPS, the outside diameter stays the same for every schedule. Only the wall thickness changes, so the inside diameter becomes smaller as the schedule increases.
What is the difference between SCH 10 and SCH 10S?
SCH 10S is the stainless steel schedule under ASME B36.19M. In many sizes it matches SCH 10, but not in all, so quote the exact schedule written on the buyer's purchase order.
Which schedule should I recommend?
It depends on pressure, temperature, corrosion allowance and the joining method. When the application is unclear, ask for the design pressure and fluid before quoting.
Key takeaways
- Schedule sets wall thickness; outside diameter stays fixed for each NPS.
- SCH 40 is the general standard, SCH 10 is light wall, SCH 80 is heavy wall.
- Higher schedules mean more weight, more pressure capacity and a higher price per metre.
- Always state NPS, NB/DN, schedule, wall thickness and the governing standard in your quotes.
Clear specifications build trust. When a buyer sees that you understand schedules perfectly, you are no longer just another supplier — you are the one they can rely on.
