ASME B36.10M vs ASTM F876/F877 (CTS)
Steel vs PEX: Steel (ASME B36.10M) vs PEX tubing (CTS)
Is PEX the same size as pipe? — the short answer is that a name is not a measurement. Of the 8 nominal sizes both standards cover, 0 share the same outer diameter and 8 do not.
- Shared sizes
- 8
- Same OD
- 0
- Different OD
- 8
- Only in steel
- 9
| Nominal | ASME B36.10M OD (in) | ASME B36.10M OD (mm) | ASTM F876/F877 (CTS) OD (in) | ASTM F876/F877 (CTS) OD (mm) | Same outside? | steel walls | PEX walls |
|---|---|---|---|---|---|---|---|
| 1/4 | 0.540 | 13.716 | 0.375 | 9.525 | no (4.191 mm apart) | Sch 40 0.088, Sch 80 0.119, STD 0.088, XS 0.119 | no wall published |
| 3/8 | 0.675 | 17.145 | 0.500 | 12.7 | no (4.445 mm apart) | Sch 40 0.091, Sch 80 0.126, STD 0.091, XS 0.126 | no wall published |
| 1/2 | 0.840 | 21.336 | 0.625 | 15.875 | no (5.461 mm apart) | Sch 10 0.083, Sch 40 0.109, Sch 80 0.147, Sch 160 0.188, STD 0.109, XS 0.147, XXS 0.294 | SDR 9 0.070 |
| 3/4 | 1.050 | 26.67 | 0.875 | 22.225 | no (4.445 mm apart) | Sch 10 0.083, Sch 40 0.113, Sch 80 0.154, Sch 160 0.219, STD 0.113, XS 0.154, XXS 0.308 | SDR 9 0.097 |
| 1 | 1.315 | 33.401 | 1.125 | 28.575 | no (4.826 mm apart) | 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 | SDR 9 0.125 |
| 1 1/4 | 1.660 | 42.164 | 1.375 | 34.925 | no (7.239 mm apart) | Sch 40 0.140, Sch 80 0.191, Sch 160 0.250, STD 0.140, XS 0.191, XXS 0.382 | no wall published |
| 1 1/2 | 1.900 | 48.26 | 1.625 | 41.275 | no (6.985 mm apart) | Sch 10 0.109, Sch 40 0.145, Sch 80 0.200, Sch 160 0.281, STD 0.145, XS 0.200, XXS 0.400 | no wall published |
| 2 | 2.375 | 60.325 | 2.125 | 53.975 | no (6.35 mm apart) | Sch 10 0.109, Sch 40 0.154, Sch 80 0.218, Sch 160 0.344, STD 0.154, XS 0.218, XXS 0.436 | no wall published |
Sizes one standard covers and the other does not
Steel only: 1/8 (0.405 in / 10.287 mm) · 2 1/2 (2.875 in / 73.025 mm) · 3 (3.500 in / 88.9 mm) · 4 (4.500 in / 114.3 mm) · 5 (5.563 in / 141.3 mm) · 6 (6.625 in / 168.275 mm) · 8 (8.625 in / 219.075 mm) · 10 (10.750 in / 273.05 mm) · 12 (12.750 in / 323.85 mm)
PEX only: 5/8 (0.750 in / 19.05 mm)
Why the two do not line up
steel and PEX sizes come from different habits of naming. Where the plastic standard grew out of “iron pipe size”, the OD is deliberately the steel OD so that fittings share a footprint; where it grew out of tubing practice, the OD is its own number and the nominal size is closer to the bore. Nothing in the name tells you which case you are in — the table does.
Full lists: ASME B36.10M chart · ASTM F876/F877 (CTS) chart. Each size page lists the sources for its own numbers.