4" Schedule 40 PVC, ABS and steel pipe are 4.500" (114.3 mm) across the outside. 4" PVC sewer pipe is smaller at 4.215", cast iron drain pipe is 4.30" to 4.38", and copper is 4.125".
4 inch pipe sizes by type
| Pipe | Outside (OD) | Inside (ID) | Wall |
|---|---|---|---|
| PVC Schedule 40 or DWV | 4.500" (114.3 mm) | n/a | 0.237" |
| PVC Schedule 80 | 4.500" (114.3 mm) | n/a | 0.337" |
| CPVC Schedule 80 (Charlotte Corzan) | 4.500" (114.3 mm) | n/a | 0.337" |
| PVC or ABS foam core drain pipe | 4.500" (114.3 mm) | n/a | 0.237" |
| PVC sewer pipe (ASTM D3034, DR 35) | 4.215" (107.1 mm) | n/a | 0.120" |
| PVC sewer and drain pipe (ASTM D2729) | 4.215" (107.1 mm) | n/a | 0.075" |
| Steel Schedule 40, black or galvanized | 4.500" (114.3 mm) | 4.026" | 0.237" |
| Steel Schedule 80 | 4.500" (114.3 mm) | 3.826" | 0.337" |
| Cast iron, no-hub | 4.38" (111.3 mm) | 3.94" | 0.19" |
| Cast iron, hub and spigot (service weight) | 4.30" (109.2 mm) | 3.94" | 0.18" |
| Copper Type K | 4.125" (104.8 mm) | 3.857" | 0.134" |
| Copper Type L | 4.125" (104.8 mm) | 3.905" | 0.110" |
| Copper Type M | 4.125" (104.8 mm) | 3.935" | 0.095" |
| Copper DWV (drain) | 4.125" (104.8 mm) | 4.009" | 0.058" |
PVC, ABS and CPVC: Charlotte Pipe’s average OD and minimum wall; its Corzan Schedule 80 CPVC is iron pipe size. Copper: the Copper Development Association’s nominal sizes. Steel: Wheatland Tube’s table. A cell marked n/a isn’t in the maker’s table. Cast iron: Charlotte Pipe’s barrel sizes and nominal wall. A no-hub pipe’s spigot end has a bead 4.44" across.
Two 4" PVC pipes can be different sizes. Charlotte Pipe’s Schedule 40 and foam core drain pipe are 4.500" across, while its thin-wall sewer pipe, made to ASTM D3034 or ASTM D2729, is 4.215". Charlotte says not to use its sewer pipe for pressure. The ASTM number printed on the pipe tells you which one you have.
Uponor’s AquaPEX straight lengths stop at 3", and Charlotte Pipe’s FlowGuard Gold CTS CPVC at 2". Charlotte’s Schedule 80 CPVC is iron pipe size: 4.500" at 4".
What fits a 4 inch pipe
- Under a toilet: Oatey’s 3" x 4" offset flanges cement over 3" pipe or fit inside 4" pipe. See toilet flange size.
- No-hub cast iron: it joins with hubless couplings (CISPI 310), and Charlotte Pipe doesn’t recommend or warrant its no-hub pipe joined with unshielded ones.
- Schedule 40 or sewer pipe: the two are 0.285" apart on the outside, so measure the pipe and read its print before you choose fittings or a coupling for it.
- Two kinds of drain pipe: PVC, cast iron and copper all differ at 4", so use a coupling made for both pipes when you join two kinds.
Measuring your pipe
Measure across an open end, or wrap a tape around the pipe and divide by 3.14. Around the outside, 4" Schedule 40 PVC is about 14.14", sewer pipe about 13.24", no-hub cast iron about 13.76" and service weight cast iron about 13.51". For smaller pipe, see how to tell pipe size.