Dimensions
| Trade size | NPS 4 · DN 100 |
|---|---|
| Schedule | Schedule 40S · also STD |
| Standard | ASME B36.19M (stainless steel pipe) |
| Outside diameter | 4.500" · 114.30 mm |
| Wall thickness | 0.237" · 6.02 mm |
| Inside diameter | 4.026" · 102.26 mm |
| Weight, plain end | not published |
ASME B36.19M (stainless steel pipe) · DN 100
4 inch Schedule 40S pipe
Outside diameter 4.500" (114.30 mm), wall 0.237" (6.02 mm), inside diameter 4.026" (102.26 mm).
Inside diameter
4.026"
102.26 mm · wall 0.237"
Why 4 inch pipe is not 4 inches
Nominal Pipe Size is a label, not a measurement. NPS 4 pipe has an outside diameter of 4.500 inches, and it keeps that outside diameter in every schedule made. What the schedule number changes is the wall: at schedule 40s the wall is 0.237 inches, so the bore comes out at 4.026 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 4
Same outside diameter of 4.500 inches throughout - only the wall and the bore move.
| Schedule | Wall (in) | ID (in) | Weight (lb/ft) |
|---|---|---|---|
| Schedule 5 | 0.083 | 4.334 | 3.92 |
| Schedule 10 | 0.120 | 4.260 | 5.62 |
| Schedule 30 | 0.188 | 4.124 | 8.67 |
| Schedule 40 | 0.237 | 4.026 | 10.8 |
| Schedule 80 | 0.337 | 3.826 | 14.98 |
| Schedule 120 | 0.438 | 3.624 | 19.02 |
| Schedule 160 | 0.531 | 3.438 | 22.53 |
| Standard wall (STD) | 0.237 | 4.026 | 10.8 |
| Extra strong (XS) | 0.337 | 3.826 | 14.98 |
| Double extra strong (XXS) | 0.674 | 3.152 | 27.57 |
| Schedule 5S | 0.083 | 4.334 | not published |
| Schedule 10S | 0.120 | 4.260 | not published |
| Schedule 80S | 0.337 | 3.826 | not published |
Frequently asked questions
What is the wall thickness of 4 inch schedule 40s pipe?
0.237 inches (6.02 mm). The outside diameter is 4.500 inches (114.30 mm) whatever the schedule, so this wall leaves an inside diameter of 4.026 inches.
What is the inside diameter of 4 inch schedule 40s pipe?
4.026 inches (102.26 mm). Inside diameter is outside diameter minus twice the wall: 4.500 - 2 x 0.237 = 4.026 inches.
Is 4 inch pipe actually 4 inches?
No. NPS 4 is a trade size, not a measurement. The pipe measures 4.500 inches across the outside and 4.026 inches across the bore in this schedule. Only the outside diameter is fixed across schedules.
Is schedule 40s the same as STD at this size?
Yes, at NPS 4. STD is the same 0.237 inch wall here. That coincidence is per size and does not hold everywhere: standard wall and schedule 40 part company above NPS 10, and extra strong and schedule 80 part company above NPS 8.
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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