Dimensions
| Trade size | NPS 3-1/2 · DN 90 |
|---|---|
| Schedule | Schedule 10S |
| Standard | ASME B36.19M (stainless steel pipe) |
| Outside diameter | 4.000" · 101.60 mm |
| Wall thickness | 0.120" · 3.05 mm |
| Inside diameter | 3.760" · 95.50 mm |
| Weight, plain end | not published |
ASME B36.19M (stainless steel pipe) · DN 90
3-1/2 inch Schedule 10S pipe
Outside diameter 4.000" (101.60 mm), wall 0.120" (3.05 mm), inside diameter 3.760" (95.50 mm).
Inside diameter
3.760"
95.50 mm · wall 0.120"
Why 3-1/2 inch pipe is not 3-1/2 inches
Nominal Pipe Size is a label, not a measurement. NPS 3-1/2 pipe has an outside diameter of 4.000 inches, and it keeps that outside diameter in every schedule made. What the schedule number changes is the wall: at schedule 10s the wall is 0.120 inches, so the bore comes out at 3.760 inches.
That is the practical consequence. Fittings, flanges, supports and threading dies are sized to the outside diameter, so they fit any schedule of the same trade size. Flow, pressure drop and anything that has to pass through the pipe depend on the inside diameter, which changes with every schedule. Order by trade size and schedule; work your hydraulics from the bore.
Other schedules in NPS 3-1/2
Same outside diameter of 4.000 inches throughout - only the wall and the bore move.
| Schedule | Wall (in) | ID (in) | Weight (lb/ft) |
|---|---|---|---|
| Schedule 5 | 0.083 | 3.834 | 3.48 |
| Schedule 10 | 0.120 | 3.760 | 4.98 |
| Schedule 30 | 0.188 | 3.624 | 7.66 |
| Schedule 40 | 0.226 | 3.548 | 9.12 |
| Schedule 80 | 0.318 | 3.364 | 12.52 |
| Standard wall (STD) | 0.226 | 3.548 | 9.12 |
| Extra strong (XS) | 0.318 | 3.364 | 12.52 |
| Schedule 5S | 0.083 | 3.834 | not published |
| Schedule 40S | 0.226 | 3.548 | not published |
| Schedule 80S | 0.318 | 3.364 | not published |
Frequently asked questions
What is the wall thickness of 3-1/2 inch schedule 10s pipe?
0.120 inches (3.05 mm). The outside diameter is 4.000 inches (101.60 mm) whatever the schedule, so this wall leaves an inside diameter of 3.760 inches.
What is the inside diameter of 3-1/2 inch schedule 10s pipe?
3.760 inches (95.50 mm). Inside diameter is outside diameter minus twice the wall: 4.000 - 2 x 0.120 = 3.760 inches.
Is 3-1/2 inch pipe actually 3-1/2 inches?
No. NPS 3-1/2 is a trade size, not a measurement. The pipe measures 4.000 inches across the outside and 3.760 inches across the bore in this schedule. Only the outside diameter is fixed across schedules.
Not published here
One schedule at NPS 3-1/2 appears in only one of the published tables cross-checked for this section, so it is named rather than printed: XXS. Everything shown above carries at least two independent sources.
Where this table stops
This table runs from NPS 1/8 to NPS 24 and stops there. ASME B36.10M itself continues to NPS 80; those larger sizes are not carried here, so a size above NPS 24 is missing rather than undefined.
Where these figures come from
Dimensions are as defined by ASME B36.19M (stainless steel pipe). This site is an independent reference and is not affiliated with, endorsed by or approved by any standards body.
Every value on this page was cross-checked against 3 independent published sources:
- ASME/ANSI B36.10/19 - carbon, alloy and stainless steel pipe dimensions - Engineering ToolBox, edition not stated (read 2026-08-27)
- Dimensions of steel and stainless steel pipes, ASME B36.10 and ASME B36.19 - Wermac, edition not stated (read 2026-08-27)
- Nominal Pipe Size - Wikipedia, revision read 2026-08-27 (read 2026-08-27)
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