NPS 12 (DN 300) Pipe — Dimensions, Schedules & Weight
Welded and seamless steel pipe per ASME B36.10M / EN 10220
NPS 12 (DN 300) pipe always has an outside diameter of 323.8 mm (12.748") — the schedule changes only the wall, from 4.57 mm at Sch 10 to 33.32 mm at Sch 160. That is the whole logic of the schedule system: OD stays constant so fittings and threads always match, while a higher schedule buys pressure capacity with a thicker wall and a smaller bore.
The most-quoted variant, Sch STD, has a 9.53 mm wall, a 304.7 mm inside diameter, and weighs 73.86 kg/m — a 6 m length is 443.1 kg. All weights below are plain-end masses from the standard formula (OD − t) × t × 0.02466.
NPS 12 (DN 300) — all schedules
| Schedule | t (mm) | t (in) | ID (mm) | kg/m | lb/ft |
|---|---|---|---|---|---|
| Sch 10 | 4.57 | 0.18 | 314.7 | 35.98 | 24.17 |
| Sch 20 | 6.35 | 0.25 | 311.1 | 49.71 | 33.4 |
| Sch 30 | 8.38 | 0.33 | 307 | 65.18 | 43.8 |
| Sch STD | 9.53 | 0.375 | 304.7 | 73.86 | 49.63 |
| Sch 40 | 10.31 | 0.406 | 303.2 | 79.7 | 53.56 |
| Sch XS | 12.7 | 0.5 | 298.4 | 97.43 | 65.47 |
| Sch 60 | 14.27 | 0.562 | 295.3 | 108.92 | 73.19 |
| Sch 80 | 17.48 | 0.688 | 288.8 | 132.04 | 88.73 |
| Sch 100 | 21.44 | 0.844 | 280.9 | 159.86 | 107.42 |
| Sch 120 / XXS | 25.4 | 1 | 273 | 186.91 | 125.6 |
| Sch 140 | 28.58 | 1.125 | 266.6 | 208.07 | 139.81 |
| Sch 160 | 33.32 | 1.312 | 257.2 | 238.68 | 160.39 |
Frequently Asked Questions
What is the outside diameter of 12" pipe?
323.8 mm (12.748 inches) — for every schedule. NPS is a nominal name, not a measurement; the actual OD of NPS 12 is larger than 12 inches for historical reasons. From NPS 14 up, OD equals the NPS in inches.
What is the wall thickness and ID of 12" Sch STD?
Sch STD has a 9.53 mm (0.375") wall, which leaves an inside diameter of 304.7 mm. The table above lists the wall and bore for every schedule of this size.
How much does 12" Sch STD pipe weigh?
73.86 kg/m (49.63 lb/ft). A 6 m length weighs 443.1 kg, a 12 m length 886.3 kg. The heaviest listed schedule, Sch 160, weighs 238.68 kg/m.
What is the difference between STD and Schedule 40?
Up to NPS 10 they are the same wall. From NPS 12 upward they split: STD stays at 9.53 mm (3/8") for all larger sizes, while Sch 40 keeps growing with the diameter. The same happens to XS and Sch 80 above NPS 8.
Values are entered from the governing standard’s published tables and cross-checked programmatically against its mass and section formulas before publication. Spotted an error? Write to advertising@metalabout.net — verified corrections ship within days. About