Standard Applied by the app plumb.water.pipe-id
Inside diameters of water pipe by nominal size
The inside diameter the velocity is computed from, per nominal size, for PEX (SDR 9), copper Type L, CPVC CTS and Schedule 40 galvanized steel.
| When | The app uses |
|---|---|
| PEX 1 in nominal ASTM F876, SDR 9 | 0.862 in |
| PEX 2 in nominal ASTM F876, SDR 9 | 1.629 in |
| PEX 3/8 in nominal ASTM F876, SDR 9 | 0.35 in |
| PEX 1/2 in nominal ASTM F876, SDR 9 | 0.475 in |
| PEX 3/4 in nominal ASTM F876, SDR 9 | 0.671 in |
| PEX 1-1/4 in nominal ASTM F876, SDR 9 | 1.054 in |
| PEX 1-1/2 in nominal ASTM F876, SDR 9 | 1.244 in |
| Copper Type L 1 in nominal ASTM B88 | 1.025 in |
| Copper Type L 2 in nominal ASTM B88 | 1.985 in |
| Copper Type L 3 in nominal ASTM B88 | 2.945 in |
| Copper Type L 3/8 in nominal ASTM B88 | 0.43 in |
| Copper Type L 1/2 in nominal ASTM B88 | 0.545 in |
| Copper Type L 3/4 in nominal ASTM B88 | 0.785 in |
| Copper Type L 1-1/4 in nominal ASTM B88 | 1.265 in |
| Copper Type L 1-1/2 in nominal ASTM B88 | 1.505 in |
| Copper Type L 2-1/2 in nominal ASTM B88 | 2.465 in |
| CPVC 1 in nominal ASTM D2846, CTS SDR 11 | 0.901 in |
| CPVC 2 in nominal ASTM D2846, CTS SDR 11 | 1.716 in |
| CPVC 1/2 in nominal ASTM D2846, CTS SDR 11 | 0.469 in |
| CPVC 3/4 in nominal ASTM D2846, CTS SDR 11 | 0.695 in |
| CPVC 1-1/4 in nominal ASTM D2846, CTS SDR 11 | 1.105 in |
| CPVC 1-1/2 in nominal ASTM D2846, CTS SDR 11 | 1.309 in |
| Galvanized steel 1 in nominal ASTM A53, Schedule 40 | 1.049 in |
| Galvanized steel 2 in nominal ASTM A53, Schedule 40 | 2.067 in |
| Galvanized steel 3 in nominal ASTM A53, Schedule 40 | 3.068 in |
| Galvanized steel 1/2 in nominal ASTM A53, Schedule 40 | 0.622 in |
| Galvanized steel 3/4 in nominal ASTM A53, Schedule 40 | 0.824 in |
| Galvanized steel 1-1/4 in nominal ASTM A53, Schedule 40 | 1.38 in |
| Galvanized steel 1-1/2 in nominal ASTM A53, Schedule 40 | 1.61 in |
| Galvanized steel 2-1/2 in nominal ASTM A53, Schedule 40 | 2.469 in |
- Source
- ASTM · F876 (PEX, SDR 9); B88 (copper Type L); D2846 (CPVC CTS, SDR 11); A53 (steel, Schedule 40) · read the public text
- Editions checked
- —
- Used by
- Water Sizing
- Amendments
No state or local amendment to this rule is on file. Not on file means the model code as written — check your jurisdiction.
An industry standard the trade builds to.
A nominal pipe size is a name, not a bore. Half-inch PEX carries water through a hole about 0.48 inches across; half-inch Type L copper through 0.545; half-inch Schedule 40 steel through 0.622. Velocity is flow divided by area, so the size suggestion has to know the bore of the material the line type is made of, and the standard each material is made to sets it.
What the app does with it
The material is read off the line type's name the way the hanger rule reads it (3/4in PEX hot, 1in Cu, 3/4in CPVC, 2in galv), the nominal size the same way, and the inside diameter comes from this table. Velocity at a candidate size is 0.4085 × gpm ÷ (inside diameter in inches)². PEX bores are Uponor's published figures for its SDR 9 AquaPEX tube (other makers print bores a few thousandths apart); they allow for the wall's plus tolerance, so they sit a little under the outside diameter less two minimum walls, which reads a slightly higher velocity, the safe side. CPVC is CTS tube to D2846, taken as the outside diameter less two minimum walls (SDR 11, with the standard's 0.068 in minimum wall at 1/2 in): the largest bore the tube can have. Copper is Type L to B88; steel is Schedule 40.
What it does not do
It does not know Type K or Type M copper, PEX-AL-PEX, or stainless: a line type in one of those gets no velocity and no suggestion until the table grows a row.
Verify against your edition
Copper Type L matched the B88 dimension table at every size, Schedule 40 steel is the standard pipe schedule, and the PEX bores are Uponor's published AquaPEX figures. For those three materials: Settled 2026-09-27 by Claude on the owner's delegation, from the dossier's research and the model code text; not checked against a printed book or a local amendment.
The CPVC rows were settled 2026-09-27 on the same basis as PEX, the average bore: the outside diameter less two average walls, where the average wall is ASTM D2846's minimum wall plus half its tolerance. The outside diameters and minimum walls (0.625 / 0.068, 0.875 / 0.080, 1.125 / 0.102, 1.375 / 0.125, 1.625 / 0.148, 2.125 / 0.193 in) were read in Charlotte Pipe's FlowGuard Gold CTS submittal; the wall tolerance (0.020 in through 1-1/2 in, 0.023 in at 2 in) was read in a secondary table of D2846, not in the standard. The rows were the largest bore before (0.489 in at 1/2 in, now 0.469), which read about 9 percent slow and could suggest a CPVC branch one size too small near the cap.
Cited by section, not reprinted: the code text belongs to its publisher. Company practice is not a rule here — it lives with your pricing.