Pipe Size Chart: OD, ID, Volume & Flow Rate
Outside diameter, inside diameter, gallons per foot and flow capacity for 1/2" through 4" pipe in copper, PEX, CPVC and PVC — with the IPC drain size and slope requirements that go with them.
Gallons per foot = ID² × 0.0408 | OD is fixed by nominal size, ID changes with schedule
Pipe Size Reference Chart
| Nominal Size | OD — IPS / Sch 40 | OD — Copper | ID Range | Gallons / ft | Gallons / 100 ft | Max Flow (GPM) |
|---|---|---|---|---|---|---|
| 1/2" | 0.840" | 0.625" | 0.485" – 0.545" | 0.010 – 0.012 | 1.0 – 1.2 | 3.3 – 4.2 |
| 3/4" | 1.050" | 0.875" | 0.700" – 0.785" | 0.020 – 0.025 | 2.0 – 2.5 | 6.9 – 8.7 |
| 1" | 1.315" | 1.125" | 0.945" – 1.049" | 0.036 – 0.045 | 3.6 – 4.5 | 12.6 – 14.8 |
| 2" | 2.375" | 2.125" | 1.935" – 2.067" | 0.153 – 0.174 | 15.3 – 17.4 | 54.1 – 60.4 |
| 3" | 3.500" | 3.125" | 3.068" | 0.384 | 38.4 | 133.1 – 133.1 |
| 4" | 4.500" | 4.125" | 4.026" | 0.661 | 66.1 | 229.1 – 229.1 |
Supply flow figures are at the 6 ft/s velocity limit. Drainage figures are at the minimum code slope, half-full. Gallons per foot is calculated from inside diameter, so it changes with material and schedule.
Detail by Pipe Size
1/2" Pipe
Water supplyOD 0.840" IPS · 0.625" copperThe standard branch line to a single fixture. 1/2" carries one fixture comfortably but starves two running at once, which is why risers are stepped up to 3/4".
| Material | Inside Diameter | Gallons / ft | Max Flow (GPM) | Typical Use |
|---|---|---|---|---|
| Copper (Type L) | 0.545" | 0.0121 | 4.2 | Fixture branch, hot and cold |
| PEX | 0.485" | 0.0096 | 3.3 | Home-run manifold drops |
| CPVC | 0.485" | 0.0096 | 3.3 | Fixture branch |
| PVC | 0.485" | 0.0096 | 3.3 | Cold water only |
3/4" Pipe
Water supplyOD 1.050" IPS · 0.875" copperThe usual trunk line in a house: feeds two to three fixtures at once, then steps down to 1/2" at each branch.
| Material | Inside Diameter | Gallons / ft | Max Flow (GPM) | Typical Use |
|---|---|---|---|---|
| Copper (Type L) | 0.785" | 0.0251 | 8.7 | Main trunk, water heater feed |
| PEX | 0.700" | 0.0200 | 6.9 | Manifold trunk |
| CPVC | 0.700" | 0.0200 | 6.9 | Main trunk |
| PVC | 0.700" | 0.0200 | 6.9 | Irrigation, cold only |
1" Pipe
Water supplyOD 1.315" IPS · 1.125" copperService entrance and main riser size for larger homes, or any run long enough that friction loss on 3/4" becomes the limiting factor.
| Material | Inside Diameter | Gallons / ft | Max Flow (GPM) | Typical Use |
|---|---|---|---|---|
| Copper (Type L) | 1.049" | 0.0449 | 14.8 | Service entrance, main riser |
| PEX | 0.945" | 0.0364 | 12.6 | Main trunk to manifold |
| CPVC | 0.945" | 0.0364 | 12.6 | Main riser |
| PVC | 0.945" | 0.0364 | 12.6 | Irrigation main |
2" Pipe
Drainage / DWVOD 2.375" IPS · 2.125" copperThe crossover size: large enough for a commercial supply main, and the standard drain for showers, tubs and laundry on the DWV side.
| Material | Inside Diameter | Gallons / ft | Max Flow (GPM) | Typical Use |
|---|---|---|---|---|
| Copper (Type L) | 1.985" | 0.1608 | 55.4 | Commercial supply main |
| PEX | 1.935" | 0.1528 | 54.1 | Large trunk main |
| PVC (Drainage) | 2.067" | 0.1743 | 60.4 | Shower, tub and laundry drain |
3" Pipe
Drainage / DWVOD 3.500" IPS · 3.125" copperThe minimum drain size for a water closet and the usual size for a residential stack serving one or two bathroom groups.
| Material | Inside Diameter | Gallons / ft | Max Flow (GPM) | Typical Use |
|---|---|---|---|---|
| PVC (Drainage) | 3.068" | 0.3840 | 133.1 | Toilet drain, branch stack |
4" Pipe
Drainage / DWVOD 4.500" IPS · 4.125" copperBuilding drain and sewer lateral size. Oversizing past 4" on residential work slows flow and lets solids settle out.
| Material | Inside Diameter | Gallons / ft | Max Flow (GPM) | Typical Use |
|---|---|---|---|---|
| PVC (Drainage) | 4.026" | 0.6613 | 229.1 | Building drain, sewer lateral |
Code References & Best Practices:
- IPC 2021 Table 610.4 — water distribution pipe sizing by fixture unit load and developed length.
- IPC 2021 Table 710.1(1) — minimum drain size by drainage fixture unit (DFU) load; a water closet requires a minimum 3" drain.
- IPC 2021 Table 704.1 — minimum slope for horizontal drainage piping: 1/4" per foot up to 2 1/2", 1/8" per foot for 3" and larger.
- UPC 2021 Table 610.3 — alternative water supply sizing method used in UPC jurisdictions; verify which code your AHJ has adopted.
- ASTM D1785 — Schedule 40 PVC dimensions; outside diameter is fixed by nominal size, so only wall thickness changes with schedule.
- ASTM B88 — copper tube (Type K, L, M); outside diameter is nominal size plus 1/8".
Size It With a Calculator
The chart above gives you the dimensions. These tools do the sizing calculation itself.
Frequently Asked Questions
What is the OD of 3 inch pipe?
Schedule 40 PVC and steel 3" pipe has an outside diameter of 3.500". Copper tube in a 3" nominal size has an outside diameter of 3.125". Outside diameter is fixed by the nominal size and does not change with schedule — only the wall thickness and therefore the inside diameter change.
What is the OD of 4 inch pipe?
Schedule 40 PVC and steel 4" pipe has an outside diameter of 4.500". Copper 4" tube measures 4.125" outside diameter. This is why a 4" PVC fitting will not slip over 4" copper.
How many gallons per foot is 4 inch pipe?
Schedule 40 4" pipe (4.026" inside diameter) holds 0.661 gallons per linear foot, or about 66 gallons per 100 feet. The formula is ID in inches squared, times 0.0408.
How do you calculate the volume of water in a pipe?
Gallons per foot equals the inside diameter in inches squared, multiplied by 0.0408. That constant comes from (π/4) × 12 cubic inches per foot ÷ 231 cubic inches per gallon. Always use inside diameter, not nominal size — a 4" pipe has a 4.026" ID in Schedule 40 but less in heavier schedules.
What is the flow rate for 1/2 inch pipe?
About 4.2 GPM in Type L copper and 3.3 GPM in PEX, CPVC or PVC, at the 6 ft/s velocity limit normally used for supply piping. That serves one fixture comfortably but not two running at once.
Is 3/4 inch pipe big enough for a house?
For a typical single-family home, yes — 3/4" is the standard distribution trunk, stepping down to 1/2" at each fixture branch. Larger homes, long runs, or low street pressure usually call for a 1" service entrance and main riser.
What is the minimum size for a toilet drain?
3 inches. IPC 2021 Table 710.1(1) assigns a water closet a minimum 3" drain, and it cannot be reduced downstream of the fixture.
What is the minimum slope for 4 inch sewer pipe?
1/8" per foot for 3" pipe and larger, per IPC 2021 Table 704.1. Pipes 2 1/2" and smaller require 1/4" per foot. Too much slope is also a problem: water outruns the solids and the line clogs.
Why does pipe size not match the actual diameter?
Nominal pipe size is a label, not a measurement. In IPS sizing the outside diameter is held constant so fittings interchange across schedules, and the wall thickness varies instead. Copper tube uses a different convention where the outside diameter is nominal size plus 1/8".
Can 2 inch pipe be used for water supply?
Yes, in commercial and multi-family work a 2" main carries roughly 55–60 GPM. In residential plumbing 2" appears almost exclusively on the drainage side, for showers, tubs and laundry standpipes.