A reducing elbow is specified by two sizes, not one.The large end carries the full ASME B16.9 centre-to-end dimension, and the small end shares the same centre mark, so the table below gives one A value per row rather than two.
That single figure is the reason a reducing elbow cannot be ordered from the small-end size alone.
All dimensions below are millimetres, transcribed from the ASME B16.9 table.
The NPS column carries the inch designation and the DN column the metric designation, so the same row serves both a drawing in inches and a purchase order in millimetres.
Long Radius Reducing Elbow Table (90 Degrees, NPS 2 to 24)
| NPS (Large x Small) | DN (Large x Small) | O.D. Large End (mm) | O.D. Small End (mm) | Centre-to-End A (mm) |
| 2 × 1 1/2 | 50 × 40 | 60.3 | 48.3 | 76 |
| 2 × 1 1/4 | 50 × 32 | 60.3 | 42.2 | 76 |
| 2 × 1 | 50 × 25 | 60.3 | 33.4 | 76 |
| 2 1/2 × 2 | 65 × 50 | 73.0 | 60.3 | 95 |
| 2 1/2 × 1 1/2 | 65 × 40 | 73.0 | 48.3 | 95 |
| 2 1/2 × 1 1/4 | 65 × 32 | 73.0 | 42.2 | 95 |
| 3 × 2 1/2 | 80 × 65 | 88.9 | 73.0 | 114 |
| 3 × 2 | 80 × 50 | 88.9 | 60.3 | 114 |
| 3 × 1 1/2 | 80 × 40 | 88.9 | 48.3 | 114 |
| 3 1/2 × 3 | 90 × 80 | 101.6 | 88.9 | 133 |
| 3 1/2 × 2 1/2 | 90 × 65 | 101.6 | 73.0 | 133 |
| 3 1/2 × 2 | 90 × 50 | 101.6 | 60.3 | 133 |
| 4 × 3 1/2 | 100 × 90 | 114.3 | 101.6 | 152 |
| 4 × 3 | 100 × 80 | 114.3 | 88.9 | 152 |
| 4 × 2 1/2 | 100 × 65 | 114.3 | 73.0 | 152 |
| 4 × 2 | 100 × 50 | 114.3 | 60.3 | 152 |
| 5 × 4 | 125 × 100 | 141.3 | 114.3 | 190 |
| 5 × 3 1/2 | 125 × 90 | 141.3 | 101.6 | 190 |
| 5 × 3 | 125 × 80 | 141.3 | 88.9 | 190 |
| 5 × 2 1/2 | 125 × 65 | 141.3 | 73.0 | 190 |
| 6 × 5 | 150 × 125 | 168.3 | 141.3 | 229 |
| 6 × 4 | 150 × 100 | 168.3 | 114.3 | 229 |
| 6 × 3 1/2 | 150 × 90 | 168.3 | 101.6 | 229 |
| 6 × 3 | 150 × 80 | 168.3 | 88.9 | 229 |
| 8 × 6 | 200 × 150 | 219.1 | 168.3 | 305 |
| 8 × 5 | 200 × 125 | 219.1 | 141.3 | 305 |
| 8 × 4 | 200 × 100 | 219.1 | 114.3 | 305 |
| 10 × 8 | 250 × 200 | 273.0 | 219.1 | 381 |
| 10 × 6 | 250 × 150 | 273.0 | 168.3 | 381 |
| 10 × 5 | 250 × 125 | 273.0 | 141.3 | 381 |
| 12 × 10 | 300 × 250 | 323.8 | 273.0 | 457 |
| 12 × 8 | 300 × 200 | 323.8 | 219.1 | 457 |
| 12 × 6 | 300 × 150 | 323.8 | 168.3 | 457 |
| 14 × 12 | 350 × 300 | 355.6 | 323.8 | 533 |
| 14 × 10 | 350 × 250 | 355.6 | 273.0 | 533 |
| 14 × 8 | 350 × 200 | 355.6 | 219.1 | 533 |
| 16 × 14 | 400 × 350 | 406.4 | 355.6 | 610 |
| 16 × 12 | 400 × 300 | 406.4 | 323.8 | 610 |
| 16 × 10 | 400 × 250 | 406.4 | 273.0 | 610 |
| 18 × 16 | 450 × 400 | 457 | 406.4 | 686 |
| 18 × 14 | 450 × 350 | 457 | 355.6 | 686 |
| 18 × 12 | 450 × 300 | 457 | 323.8 | 686 |
| 18 × 10 | 450 × 250 | 457 | 273.0 | 686 |
| 20 × 18 | 500 × 450 | 508 | 457 | 762 |
| 20 × 16 | 500 × 400 | 508 | 406.4 | 762 |
| 20 × 14 | 500 × 350 | 508 | 355.6 | 762 |
| 20 × 12 | 500 × 300 | 508 | 323.8 | 762 |
| 20 × 10 | 500 × 250 | 508 | 273.0 | 762 |
| 24 × 22 | 600 × 550 | 610 | 559 | 914 |
| 24 × 20 | 600 × 500 | 610 | 508 | 914 |
| 24 × 18 | 600 × 450 | 610 | 457 | 914 |
| 24 × 16 | 600 × 400 | 610 | 406.4 | 914 |
| 24 × 14 | 600 × 350 | 610 | 355.6 | 914 |
| 24 × 12 | 600 × 300 | 610 | 323.8 | 914 |
How to Read the Centre-to-End Column
Centre-to-End, A, is measured from the centre line of the fitting to the end face of the large end. Because the small end sits on the same centre line, the drawing dimension A applies to the large end only; the small-end face position follows from the fitting geometry, not from a second tabulated value.
- A for NPS 2 is 76 mm, for NPS 4 is 152 mm, for NPS 6 is 229 mm, and for NPS 12 is 457 mm: the value scales with the large-end size, which is why 2 x 1 and 2 x 1 1/2 share the same 76 mm.
- NPS 20 rows carry A = 762 mm and NPS 24 rows carry A = 914 mm, again set by the large end.
- The small-end outside diameter is the bevel dimension used for fit-up; it is the pipe OD of the smaller size, not a fitting dimension.
- Tolerances on these dimensions follow ASME B16.9, not the table itself: the table gives nominal geometry only.
What the Table Does Not Tell You
Three things a buyer usually asks for are not in the B16.9 dimensional table and have to be specified separately:
- Wall thickness and schedule. B16.9 sizes fittings to match the pipe schedule ordered (SCH10, SCH40, SCH80, or custom wall), and the bevel thickness is taken from that schedule.
- Weight. Calculated from the finished geometry and wall thickness by the manufacturer, not tabulated in the standard.
- Material grade and its specification, for example ASTM A234 WPB, A403 WP304L, or A815 WPS32205. The same dimensional row is used for every grade.
The full datasheet is available as a download: ASME B16.9 long radius reducing elbows PDF. For the straight-size counterpart, see the stainless steel pipe and buttweld fitting range, or send the isometric for a fit-up check against these dimensions.
