ASTM F876/F877 (CTS) ·size chart
CTS 1 outer diameter: 1.125 in / 28.575 mm
- OD (inches)
- 1.125 in
- OD (millimetres)
- 28.575 mm
- DN
- 25
- Wall range
- 0.125–0.125 in
- Bore range
- 0.875–0.875 in
Crosslinked polyethylene tubing in CTS (copper tube size) ODs, designated by SDR rather than schedule. For CTS 1, ASTM F876/F877 (CTS) fixes the outside at 1.125 in / 28.575 mm; the 1 published wall series below are what change the bore.
| Wall series | Wall (in) | Wall (mm) | ID (in) | ID (mm) | Bore is | ≈ kg/m |
|---|---|---|---|---|---|---|
| SDR 9 | 0.125 | 3.175 | 0.875 | 22.225 | a maximum | 0.24 |
Same body, different material. steel 1 Sch 40 = STD, and PVC 1 Sch 40, and stainless 1 Sch 40S are the same 0.133 in wall on the same 1.315 in / 33.401 mm body; steel 1 Sch 80 = XS, and PVC 1 Sch 80, and stainless 1 Sch 80S are the same 0.179 in wall on the same 1.315 in / 33.401 mm body. A caliper cannot separate them — what the pipe is made of does.
The same nominal label in other standards
| Standard | OD (in) | OD (mm) | DN | Published wall series |
|---|---|---|---|---|
| ASME B36.10M · welded and seamless steel pipe | 1.315 | 33.401 | 25 | Sch 10 0.109 · Sch 40 0.133 · Sch 80 0.179 · Sch 160 0.250 · STD 0.133 · XS 0.179 · XXS 0.358 |
| ASTM D2241 · PVC pressure pipe | 1.315 | 33.401 | 25 | Sch 40 0.133 · Sch 80 0.179 |
| ASTM F876/F877 (CTS) · PEX tubing (CTS) | 1.125 | 28.575 | 25 | SDR 9 0.125 |
| ASME B36.19M · stainless steel pipe | 1.315 | 33.401 | 25 | Sch 5S 0.065 · Sch 10S 0.109 · Sch 40S 0.133 · Sch 80S 0.179 |
PEX vs steel — 1 (ASME B36.10M) · PEX vs PVC — 1 (ASTM D2241)
Measuring this size
- Measure across the pipe, not the fitting: that is the OD, and it is the number a clamp, a hole saw or an insulation sleeve has to match.
- Measured
28.575± a fraction of a millimetre points at CTS 1. Check which standards a measurement fits — the same OD can belong to more than one. - The bore decides flow; the wall decides pressure rating and how deep a thread cuts. Neither number is in the name CTS 1 carries.
Questions about CTS 1
What is the outer diameter of CTS 1 pipe?
1.125 in / 28.575 mm — but that is only true for ASTM F876/F877 (CTS). The same nominal label in ASME B36.10M (1.315 in / 33.401 mm) and ASTM D2241 (1.315 in / 33.401 mm) and ASME B36.19M (1.315 in / 33.401 mm) is a different pipe. Calipers measure this number; the name does not.
What is the inside diameter of CTS 1 SDR 9?
0.875 in / 22.225 mm — the outer diameter minus twice the wall (1.125 − 2 × 0.125). This standard publishes a MINIMUM wall, so the bore is a maximum: a thicker pipe has a smaller bore. Other wall series for this size are in the table above.
Is CTS 1 the same as DN 25?
DN 25 is the millimetre-family name for this size, so yes for the size — no for the number. DN is not the outer diameter and not the bore; CTS 1 measures 1.125 in / 28.575 mm outside. See the NPS ↔ DN table for the whole series.
Sources for these numbers
- PEX Universe
- Viega PureFlow technical data (ASTM F876/F877 CTS-OD SDR-9)
- checked 2026-09-25
Each wall value in this page's tables was confirmed by two independent publications; the list above is those pairs combined, so a source appears once even when it supports several rows. The outer diameter is published per size, not per wall. Data version 48d86b977106.
No edition year is claimed. These values match ASTM F876/F877 (CTS) as published by the sources above, but the specific printing was not verified, so the standard is named without a year.
Next
- Full ASTM F876/F877 (CTS) chart (9 sizes)
- OD / ID / wall calculator — measure two, get the third
- About ASTM F876/F877 (CTS)