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
At the defaults — 100 ft of 2 in Schedule 40 pipe — the run holds 17.4 gallons (66 L), weighing about 145 lb; the full chain is in the worked example below. The one input that matters is the inner diameter, not the size on the label — and because volume goes with the bore squared, doubling the diameter quadruples the water.
Nominal size vs inner diameter — why the bore rules
Water lives in the bore, and the number stamped on a pipe is a name, not that bore. The same “2 inch” label hides very different inner diameters across materials:
- Schedule 40 (steel / PVC): a “2 in” pipe measures 2.067 in inside — the presets here use the published Sch 40 IDs.
- Copper (type L): sized by outside diameter with thinner walls, so its bore differs from Sch 40 at the same nominal size.
- PEX: runs a smaller bore than copper or Sch 40 for the same nominal — a real difference over long hot-water runs.
- DWV & Schedule 80: drain pipe and thicker-walled Sch 80 change the bore again — type the ID from the spec sheet for anything but Sch 40.
The reason it matters is that the error compounds. Guess the bore a sixteenth of an inch high on a 100 ft run and the volume is off by more than you would expect, because area follows the radius squared — a small diameter mistake becomes a real gallons mistake once it is multiplied by a long length. When accuracy counts, read the ID off the print rather than the label on the pipe.
What you use each pipe size for
Size follows flow — small bores for fixtures, big ones for mains and drains. The everyday residential run:
- 1/2 in: the branch to a single fixture — a sink, a toilet, a hose bibb.
- 3/4 in: supply mains and multi-fixture branches; the common outdoor and manifold size.
- 1–1½ in: larger mains, irrigation zones, and pump work.
- 2 in: the default here — mains, pool and spa lines, and bathroom-group drains.
- 3–4 in: building drains, sewer laterals, and the runs that dominate a system-volume total.
Volume is only half the reason to know a pipe’s bore; flow velocity is the other. Push too much water through an undersized pipe and it turns noisy and erodes copper over time, which is why supply mains step up before they branch down. This tool answers the volume question — how much water the run holds, for filling, draining, chlorinating or figuring the weight on a hanger.
Gallons per foot of pipe (Schedule 40)
Table 1 is volume per foot for every nominal Sch 40 size; Table 2 multiplies the common ones out to a 100 ft run, the length people ask about most.
| 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 |
| Nominal | Gallons |
|---|---|
| 3/4″ | 2.77 |
| 1″ | 4.49 |
| 2″ | 17.43 |
| 4″ | 66.13 |
How to measure a pipe run’s volume
- Total the run length in feet — add up every straight length of the same size, end to end.
- Get the true inner diameter — pick a Schedule 40 preset, or type the ID from the pipe’s spec for copper, PEX or DWV.
- Set the number of identical runs if you’re totalling several the same size at once.
- Read gallons, liters and weight; the per-foot figure lets you size a drain-down bucket in your head.
- Total different sizes separately and add them, then round the system volume up for dosing or filling.
Worked example: water in 100 ft of 2 in pipe
The default, worked line by line — 100 ft of 2 in Schedule 40, inner diameter 2.067 in:
area = π × 0.0861² = 0.0233 ft²
volume = 0.0233 × 100 = 2.33 ft³
water = 2.33 × 7.48 = 17.4 gal · × 62.4 = 145 lb
Per foot that is 0.174 gallons, the number worth memorizing for 2 in pipe. Weight is the line people forget: 145 lb of water in an overhead run is real load on the hangers, and a reason to know the volume before a drain-down or a pressure test.
What this pipe volume doesn’t include
This is the straight-run water volume — the bulk of most systems, but not the whole of any:
- Fittings. Elbows, tees and couplings each hold a little; across a big system it adds up.
- Valves and meters. Their internal volume is small but real on a dosing calculation.
- Equipment. Tanks, filters, water heaters and pumps hold far more than the pipe — total them separately.
- Pipe wall. This is the water content, not the pipe’s own weight or its outside dimensions.
- Air and slope. Drain lines run partly full, so their water content is less than the bore volume.
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.
How much water is in 100 feet of 1 inch pipe?
About 4.5 gallons for 1 in Schedule 40 (ID 1.049 in) — 0.045 gallons per foot — weighing roughly 37 lb. It is a quarter of what a 2 in run of the same length holds, because volume follows the bore squared, not the nominal size.
Sources and standards
The volume is exact geometry; the presets come from published pipe dimensions and water constants:
- Schedule 40 inner diameters: the published Sch 40 IDs (2 in = 2.067 in) behind the size presets.
- Water constants: 7.48052 gallons and 62.4 lb per cubic foot, 8.34 lb per gallon — standard at room temperature.
- Bore-squared geometry: volume = π r² × length, so it scales with the diameter squared.
- The spec sheet governs: copper, PEX, DWV and Sch 80 all differ — type the real ID for anything but Sch 40.
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