Plumber's Pocket Card — Pipe Dimensions, C Factors & Gas Capacity
One-page plumber's card: Schedule 40/80 steel pipe dimensions, Hazen-Williams C factors, gas pipe capacities, and water heater sizing.
Updated August 20, 2026
Four lookups that cover most rough-in questions, on one printable card: ASME B36.10M steel pipe outside diameters with Schedule 40 and 80 walls and bores for the common trade sizes, the Hazen-Williams roughness coefficients that drive friction-loss math, the NFPA 54 natural gas capacity table for Schedule 40 pipe at low pressure, and the DOE water heater sizing numbers for both tank and tankless selection.
Every cell is generated from the constants behind the pipe schedules chart and the Hazen-Williams, gas pipe sizing, and water heater sizing calculators — pipe bores are computed as OD − 2 × wall, never copied. Print it for the truck; the linked calculators handle demand totals, pressure drops, and the longer runs this card trims for space.
Plumber's Pocket Card — Pipe Dimensions, C Factors & Gas Capacity — updated August 20, 2026
Steel pipe Sch 40/80 (ASME B36.10M)
| NPS | OD (in) | S40 wall | S40 ID | S80 wall | S80 ID |
|---|---|---|---|---|---|
| 1/2" | 0.840 | 0.109 | 0.622 | 0.147 | 0.546 |
| 3/4" | 1.050 | 0.113 | 0.824 | 0.154 | 0.742 |
| 1" | 1.315 | 0.133 | 1.049 | 0.179 | 0.957 |
| 1-1/4" | 1.660 | 0.140 | 1.380 | 0.191 | 1.278 |
| 1-1/2" | 1.900 | 0.145 | 1.610 | 0.200 | 1.500 |
| 2" | 2.375 | 0.154 | 2.067 | 0.218 | 1.939 |
| 2-1/2" | 2.875 | 0.203 | 2.469 | 0.276 | 2.323 |
| 3" | 3.500 | 0.216 | 3.068 | 0.300 | 2.900 |
| 3-1/2" | 4.000 | 0.226 | 3.548 | 0.318 | 3.364 |
| 4" | 4.500 | 0.237 | 4.026 | 0.337 | 3.826 |
NPS 1/2″–4″; ID computed as OD − 2 × wall. Full 1/8″–12″ table with Sch 160, PVC, and copper: pipe schedules chart.
Hazen-Williams C factors
| Material | C |
|---|---|
| PVC / plastic | 150 |
| Copper | 140 |
| Ductile iron (cement-lined, new) | 140 |
| Concrete | 130 |
| Galvanized steel | 120 |
| Cast iron (old, unlined) | 100 |
New-pipe values except where noted; higher C = smoother pipe, less friction loss.
Natural gas capacity, CFH (NFPA 54 Table 402.4(2))
| Run (ft) | 1/2" | 3/4" | 1" | 1-1/4" | 1-1/2" | 2" |
|---|---|---|---|---|---|---|
| 10 | 172 | 360 | 678 | 1390 | 2090 | 4020 |
| 20 | 118 | 247 | 466 | 957 | 1430 | 2760 |
| 30 | 95 | 199 | 374 | 768 | 1150 | 2220 |
| 40 | 81 | 170 | 320 | 657 | 985 | 1900 |
| 50 | 72 | 151 | 285 | 583 | 873 | 1680 |
| 60 | 65 | 137 | 258 | 528 | 791 | 1520 |
| 70 | 60 | 126 | 237 | 486 | 728 | 1400 |
| 80 | 56 | 117 | 220 | 452 | 677 | 1300 |
| 90 | 52 | 110 | 207 | 424 | 635 | 1220 |
| 100 | 50 | 105 | 197 | 404 | 605 | 1170 |
Sch 40 metallic pipe, natural gas SG 0.60, inlet < 2 psi, 0.5 in w.c. drop. Runs of 125–200 ft: gas pipe sizing calculator.
Tank sizing — gal of hot water per use (DOE)
| Use | gal |
|---|---|
| Shower | 20 |
| Shaving | 2 |
| Hand dish / food prep | 3 |
| Dishwasher | 7 |
| Washer (top-load) | 25 |
| Washer (H-axis) | 15 |
Sum the busiest hour for first-hour rating (FHR); pick a tank with FHR within a couple of gallons.
Tankless sizing — simultaneous demand (gpm)
| Fixture | gpm |
|---|---|
| Shower | 2.0 |
| Kitchen sink | 1.5 |
| Bathroom sink (lavatory) | 1.0 |
| Clothes washer | 2.0 |
| Dishwasher | 1.5 |
Representative flows, not code values. Add the fixtures that run at once, then match gpm at your temperature rise.
Sources
- ASME B36.10M steel pipe OD and Sch 40/80 walls; ID = OD − 2 × wall
- Published Hazen-Williams coefficient tables (Engineers Edge / CECALC)
- NFPA 54 / IFGC Table 402.4(2), Schedule 40 pipe, 0.5 in w.c. drop
- DOE water heater sizing worksheet values
Try the Calculators
Plumber's Pocket Card — Pipe Dimensions, C Factors & Gas Capacity — reuven.tools/cheat-sheets/plumber-pocket-card — verified against: ASME B36.10M steel pipe OD and Sch 40/80 walls; ID = OD − 2 × wall; Published Hazen-Williams coefficient tables (Engineers Edge / CECALC); NFPA 54 / IFGC Table 402.4(2), Schedule 40 pipe, 0.5 in w.c. drop; DOE water heater sizing worksheet values