NPS 11 Pipe Dimensions
Outside diameter 11.750 in (298.4 mm) — fixed across every schedule. 4 wall thicknesses from a distributor's stock chart, with bore, weight, flow and pressure capacity for each, and the flanges and fittings that go with the size.
Not an ASME B36.10 size. NPS 11 does not appear in the 2004, 2015 or 2022 editions of ASME B36.10. It is an obsolete trade size. The dimensions on this page come from a single distributor's stock chart and have not been confirmed against a second source. Use them to identify old pipe, not to specify new.
- Nominal size
- NPS 11
- Metric designator
- DN 275
- Outside diameter
- 11.750 in (298.4 mm)
- Schedules listed
- 4
- Standard weight wall
- 0.375 in (9.5 mm)
- Extra strong wall
- 0.500 in (12.7 mm)
What NPS 11 is
NPS 11 pipe measures 11.750 in (298.4 mm) across the outside, which is 0.750 in more than the 11 in its name suggests. Below NPS 14 the designation is a label inherited from iron pipe sizing and matches neither the outside diameter nor the bore of any schedule exactly. The metric designator is DN 275, which is likewise a label and not a measurement in millimetres. Whatever the schedule, the outside diameter stays at 11.750 in (298.4 mm): a heavier wall grows inward and takes the difference out of the bore.
An obsolete trade size that is not in ASME B36.10. B16.5 publishes no flange for it and B16.9 no fitting.
Every schedule in NPS 11
Dimensions are given in inches, with the millimetre equivalent beneath in grey.
| Schedule | Wall thickness | Inside diameter | Weight, empty | Weight, water filled | Flow area (in²) | Water (US gal/ft) |
|---|---|---|---|---|---|---|
| Sch 40 | 0.3759.52 mm | 11.000279.40 mm | 45.6067.86 kg/m | 86.80129.17 kg/m | 95.03 | 4.937 |
| STD | 0.3759.52 mm | 11.000279.40 mm | 45.6067.86 kg/m | 86.80129.17 kg/m | 95.03 | 4.937 |
| Sch 80 | 0.50012.70 mm | 10.750273.05 mm | 60.1389.48 kg/m | 99.48148.04 kg/m | 90.76 | 4.715 |
| XS | 0.50012.70 mm | 10.750273.05 mm | 60.1389.48 kg/m | 99.48148.04 kg/m | 90.76 | 4.715 |
Inside diameter is OD − 2t. Weight is calculated for carbon steel as w = 10.69 × t × (OD − t) lb/ft and is the plain-end weight, excluding coatings, linings and fittings. Water-filled weight adds fresh water at 8.3454 lb per US gallon.
Reading the table
The chart lists 4 designations in NPS 11, which between them give 2 different wall thicknesses. The lightest is Schedule 40 at 0.375 in (9.5 mm) and the heaviest is Schedule 80 at 0.500 in (12.7 mm). Going from one to the other takes the bore from 11.000 in (279.4 mm) down to 10.750 in (273.1 mm), which cuts the flow area by 4% and raises the weight from 45.60 to 60.13 lb/ft, a factor of 1.3.
Standard weight equals Schedule 40 in this size. Extra strong equals Schedule 80. Where two designations share a wall they are the same pipe under two names, and either may appear on a mill certificate. The match is specific to the size, so it is the wall thickness in inches that should go on a requisition, not the designation alone.
For handling and support loads, a 20 ft length of standard weight NPS 11 pipe weighs about 912 lb (414 kg) empty and 1736 lb (787 kg) full of water. The water-filled figure is the one that governs pipe support spacing and the load during a hydrostatic test, including on lines that will carry gas or vapour in service.
Flow and pressure capacity by schedule
Two questions decide a schedule: how much the bore will carry, and how much pressure the wall will hold. The flow columns give the water flow through each bore at three velocities that bracket ordinary liquid service, from a pump suction line at the low end to a pump discharge line at the high end. The pressure columns are the ASME B31.3 pressure design equation solved for pressure, first on the nominal wall and then on the wall after the 12.5% mill under-tolerance that seamless pipe is allowed.
| Schedule | Flow at 3 ft/s (US gpm) | Flow at 6 ft/s (US gpm) | Flow at 10 ft/s (US gpm) | Pressure, nominal wall | Pressure, wall less 12.5% |
|---|---|---|---|---|---|
| Sch 40 | 888.6 | 1,777.2 | 2,962.1 | 1,310 psig | 1,143 psig |
| STD | 888.6 | 1,777.2 | 2,962.1 | 1,310 psig | 1,143 psig |
| Sch 80 | 848.7 | 1,697.4 | 2,829.0 | 1,762 psig | 1,535 psig |
| XS | 848.7 | 1,697.4 | 2,829.0 | 1,762 psig | 1,535 psig |
Flow is velocity × flow area. Pressure is P = 2·S·t / (D − 2·Y·t) with S = 20,000 psi, E = W = 1.0 and Y = 0.4: seamless carbon steel such as A106 Gr B at moderate temperature, with no corrosion allowance and no threading allowance. It is an illustration of the arithmetic, not a design rating.
The method behind both halves of that table is set out in the pipe sizing guide and the wall thickness guide, each with a worked example.
Flanges for NPS 11 pipe
ASME B16.5 publishes no flange in NPS 11 and ASME B16.9 no buttweld fitting. That is the practical meaning of an obsolete size: pipe of this diameter exists in old plant, but nothing standard is made to connect to it. New work uses the next size up or down.
Guides and comparisons for this page
NPS 11 in each schedule chart
Common questions
What is the outside diameter of NPS 11 pipe?
NPS 11 pipe has an outside diameter of 11.750 in (298.4 mm). That outside diameter is fixed: it is identical in every schedule, and only the wall thickness — and therefore the bore — changes from one schedule to the next.
What is the inside diameter of NPS 11 schedule 40 pipe?
11.000 in (279.4 mm). The 0.375 in (9.5 mm) wall comes off the 11.750 in (298.4 mm) outside diameter twice, once on each side, which leaves that bore and a flow area of 95.03 in².
How much does NPS 11 schedule 40 pipe weigh?
45.60 lb/ft (67.86 kg/m) as plain-end carbon steel, on a wall thickness of 0.375 in (9.5 mm). It holds 4.937 US gallons of water per foot.
What is the metric equivalent of NPS 11?
DN 275. DN is a dimensionless designator, not a measurement — DN 275 pipe does not measure 275 mm anywhere. Its actual outside diameter is 298.4 mm.