Short definition
Schedule 40 vs Schedule 80 is a comparison of wall thickness in PVC and CPVC pipe. Same outside diameter, different inside diameter and wall — Sch 80 has a thicker wall, smaller flow ID, and higher pressure rating. The decisive practical rule: Schedule 40 must not be threaded; threaded connections require Schedule 80 (or thicker).
What it is
For 1-inch nominal PVC at 73°F:
- Schedule 40 — wall ~0.133 inch, ID ~1.049 inch, pressure rating around 450 psi (per ASTM D1785).
- Schedule 80 — wall ~0.179 inch, ID ~0.957 inch, pressure rating around 630 psi.
The threading rule is the part most homeowners run into. Threading a Sch 40 PVC fitting removes too much wall material and creates a stress concentration that fails. Threaded PVC connections — at brass valves, pump inlets, hose bibs, anywhere male-threaded transitions are needed — require Sch 80 (or thicker) on the threaded end.
In practice, many residential installs run Sch 40 PVC for the bulk of the work, with a Sch 80 male adapter at any threaded interface.
Why it matters to a homeowner
DIY irrigation manifolds are the classic application. Sch 40 PVC for buried laterals, Sch 80 for any threaded transition or above-ground exposed section that has to hold pressure. Pool and spa supply lines often spec Sch 80 throughout for higher temperature and pressure margins. When buying threaded PVC fittings at the hardware store, check the schedule — Sch 40 threaded fittings exist in the bin but shouldn’t be used in pressure service.
Color isn’t a reliable indicator (different brands use different colors); read the printed label on the pipe.