ASTM D2241 vs ASTM F876/F877 (CTS)
PVC vs PEX: PVC (ASTM D2241) vs PEX tubing (CTS)
Do PVC and PEX fittings interchange? — the short answer is that a name is not a measurement. Of the 5 nominal sizes both standards cover, 0 share the same outer diameter and 5 do not.
- Shared sizes
- 5
- Same OD
- 0
- Different OD
- 5
- Only in PVC
- 4
| Nominal | ASTM D2241 OD (in) | ASTM D2241 OD (mm) | ASTM F876/F877 (CTS) OD (in) | ASTM F876/F877 (CTS) OD (mm) | Same outside? | PVC walls | PEX walls |
|---|---|---|---|---|---|---|---|
| 1/2 | 0.840 | 21.336 | 0.625 | 15.875 | no (5.461 mm apart) | Sch 40 0.109, Sch 80 0.147 | SDR 9 0.070 |
| 3/4 | 1.050 | 26.67 | 0.875 | 22.225 | no (4.445 mm apart) | Sch 40 0.113, Sch 80 0.154 | SDR 9 0.097 |
| 1 | 1.315 | 33.401 | 1.125 | 28.575 | no (4.826 mm apart) | Sch 40 0.133, Sch 80 0.179 | SDR 9 0.125 |
| 1 1/2 | 1.900 | 48.26 | 1.625 | 41.275 | no (6.985 mm apart) | Sch 40 0.145, Sch 80 0.200 | no wall published |
| 2 | 2.375 | 60.325 | 2.125 | 53.975 | no (6.35 mm apart) | Sch 40 0.154, Sch 80 0.218 | no wall published |
Sizes one standard covers and the other does not
PVC only: 3 (3.500 in / 88.9 mm) · 4 (4.500 in / 114.3 mm) · 6 (6.625 in / 168.275 mm) · 8 (8.625 in / 219.075 mm)
PEX only: 1/4 (0.375 in / 9.525 mm) · 3/8 (0.500 in / 12.7 mm) · 5/8 (0.750 in / 19.05 mm) · 1 1/4 (1.375 in / 34.925 mm)
Why the two do not line up
PVC 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: ASTM D2241 chart · ASTM F876/F877 (CTS) chart. Each size page lists the sources for its own numbers.