How this pipe volume calculator works
A pipe is a cylinder of water, so volume is bore area times length. The one trap is the bore: nominal pipe size is a name, not a measurement, and the calculator works from the true inner diameter:
gallons = ft³ × 7.4805 · liters = ft³ × 28.317 · weight = ft³ × 62.4 lb
Worked example: water in 100 ft of 2 in pipe
2 in Schedule 40 has a 2.067 in bore — 0.0233 ft² of cross-section. Over 100 ft that's 2.33 ft³: 17.4 gallons (66 L), weighing about 145 lb. Per foot, remember 0.174 gal and you can size a drain-down bucket in your head.
Gallons per foot of pipe (Schedule 40)
| Nominal | Inner Ø | Gal / ft |
|---|---|---|
| 1/2″ | 0.622″ | 0.0158 |
| 3/4″ | 0.824″ | 0.0277 |
| 1″ | 1.049″ | 0.0449 |
| 1-1/4″ | 1.380″ | 0.0777 |
| 1-1/2″ | 1.610″ | 0.1058 |
| 2″ | 2.067″ | 0.1743 |
| 3″ | 3.068″ | 0.3840 |
| 4″ | 4.026″ | 0.6613 |
Pipe volume FAQ
How much water is in 100 feet of 2 inch pipe?
About 17.4 gallons for 2 in Schedule 40 (ID 2.067 in) — 0.174 gallons per foot, weighing about 145 lb. The same run in 4 in pipe holds 66 gallons; in 3/4 in, under 3.
How many gallons per foot of pipe?
For Schedule 40: 1/2″ holds 0.016 gal/ft, 3/4″ 0.028, 1″ 0.045, 1-1/2″ 0.106, 2″ 0.174, 3″ 0.384, and 4″ 0.661. The chart on this page lists them; the calculator computes any custom bore.
Why does the calculator ask for inner diameter, not pipe size?
Because water lives in the bore. A "2 inch" Schedule 40 pipe measures 2.067 in inside; copper, PEX and DWV all run different inner diameters for the same nominal size. Pick a Sch 40 preset or type the ID from your pipe's spec sheet.
Does pipe volume include fittings and valves?
No — this is the straight-run volume. Fittings add a little and equipment like tanks and filters add a lot, so for chlorination, glycol or chemical dosing, total the runs here and round the system volume up.
How much does water in pipe weigh?
Water weighs 62.4 lb per cubic foot — 8.34 lb per gallon. The default 100 ft of 2 in pipe carries about 145 lb of water, which matters for hangers, drain-downs, and anything overhead.
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