Pipe Volume Calculator
This is the volume of a clear, full pipe. Blockages, sediment buildup, or a partially filled line will hold less.
A pipe holds about 0.0408 × ID² gallons per foot, with the inside diameter (ID) in inches: roughly 0.16 gal/ft for a 2-inch pipe, 0.65 gal/ft for 4-inch, 1.47 gal/ft for 6-inch and 2.61 gal/ft for 8-inch, so a full 100-foot run of 4-inch pipe holds about 65.3 gallons. Enter your pipe’s inside diameter (ID) and total length below for the full capacity in gallons, liters, and cubic feet.
Pipe Volume Chart: Gallons per Foot by Size
| Inside diameter | Gallons per foot | Gallons per 100 ft | Liters per meter |
|---|---|---|---|
| 1/2" ID | 0.010 gal | 1.0 gal | 0.13 L |
| 3/4" ID | 0.023 gal | 2.3 gal | 0.29 L |
| 1" ID | 0.041 gal | 4.1 gal | 0.51 L |
| 1-1/4" ID | 0.064 gal | 6.4 gal | 0.79 L |
| 1-1/2" ID | 0.092 gal | 9.2 gal | 1.14 L |
| 2" ID | 0.163 gal | 16.3 gal | 2.03 L |
| 3" ID | 0.367 gal | 36.7 gal | 4.56 L |
| 4" ID | 0.653 gal | 65.3 gal | 8.11 L |
| 6" ID | 1.47 gal | 146.9 gal | 18.24 L |
| 8" ID | 2.61 gal | 261.1 gal | 32.43 L |
| 10" ID | 4.08 gal | 408.0 gal | 50.67 L |
| 12" ID | 5.88 gal | 587.5 gal | 72.97 L |
How pipe volume works
A pipe is a cylinder, so its volume follows the same formula: the area of the circular cross-section times the length of the run. Get the inside diameter and the length right and the rest is arithmetic.
Measure the inside, not the outside
The most common mistake is measuring the outside diameter (OD) of the pipe, often taken straight off the label. Thicker-walled pipe like Schedule 80 has a smaller bore, so a 4-inch OD segment might have only about a 3-inch inside diameter. Volume depends on the inside diameter, so that's the number to use.
Inside diameter by pipe material and schedule
The nominal size printed on a pipe names the fitting standard, not the bore. Two pipes labelled 3/4-inch can hold noticeably different amounts of water because their walls differ, and the water only sees the inside diameter. That's why a PVC water pipe, a copper line, and a PEX run of the "same" size don't hold the same volume. Look up the actual ID for your material below, then enter that number above.
| Nominal size | PVC Sch 40 | PVC Sch 80 | Copper Type L | PEX (SDR-9) |
|---|---|---|---|---|
| 1/2 in | 0.622 | 0.546 | 0.545 | 0.475 |
| 3/4 in | 0.824 | 0.742 | 0.785 | 0.671 |
| 1 in | 1.049 | 0.957 | 1.025 | 0.862 |
| 2 in | 2.067 | 1.939 | — | — |
| 4 in | 4.026 | 3.826 | — | — |
PVC and CPVC water pipe
Schedule 40 is the everyday white PVC for cold-water supply, drains, and irrigation; Schedule 80 shares the same outside diameter but has a thicker wall for higher pressure, which shrinks the bore. At 4-inch nominal that's a 4.026-inch ID for Schedule 40 versus 3.826 inches for Schedule 80 — enough to drop the volume of a 100-foot run from about 65 gallons to roughly 59. CPVC used for hot water follows the same OD-controlled sizing, so read its ID off the print line the same way.
Copper pipe
Copper comes in Type M (thin wall), Type L (medium, the common residential choice), and Type K (thick). All three share an outside diameter at a given nominal size, so the thicker the wall, the smaller the bore and the less it holds. Type L 3/4-inch has about a 0.785-inch ID; the thinner Type M runs slightly larger at 0.811 inch. The difference is small per foot but adds up over a long run.
PEX pipe
PEX holds the least of the three at any nominal size. It's sized by copper tube size (CTS) on the outside so it fits standard fittings, but its wall is proportionally thick, so 3/4-inch PEX has only about a 0.671-inch ID — close to a third less cross-section than 3/4-inch Schedule 40 PVC. If you size a recirculation loop or estimate purge volume from the PVC or copper figure, PEX will come out over.
Gas pipe
For natural gas or propane, the same cylinder math gives the pipe's internal volume, but that volume is a gas capacity, not gallons of liquid. It matters for purge and leak-down calculations rather than water delivery. Black iron and steel gas pipe is sized like Schedule 40, so its ID matches the Schedule 40 column above; CSST and other systems have their own bore charts. Gas sizing itself is driven by pressure and BTU load over distance, not by static volume, so treat the volume figure as informational only and follow the fuel-gas code for line sizing.
Where the estimate needs judgment
- Partly full lines. A gravity drain or sewer line rarely runs full. The calculator gives full-pipe capacity; a line flowing half-full holds about half that, and the wetted area of a partially filled circle isn't linear with depth.
- Scale and buildup. Old galvanized and cast-iron pipe narrows as scale, rust, and grease collect. A 30-year-old 1-inch line can behave like a 3/4-inch one, so the nominal ID overstates what it actually holds and passes.
- Mixed runs. A real system changes diameter at meters, manifolds, and fixture drops. Calculate each straight segment at its own ID and length, then add the volumes rather than averaging one diameter across the whole run.
- Fittings and valves. Elbows, tees, and valve bodies each hold a little extra. For most jobs, measuring point to point along the centerline absorbs this; for precise purge or dosing volumes, add the manufacturer's fitting allowances.
About these figures: the volume math is the standard cylinder formula (π × radius² × length), with 231 cubic inches per U.S. gallon and 1,728 per cubic foot from NIST. Inside-diameter values follow published dimension standards — Schedule 40/80 PVC and Type L copper from manufacturer and Engineering ToolBox dimension tables, and SDR-9 PEX per ASTM F876 (see Sources). Actual bore varies slightly by brand and production tolerance, so measure or check the print line when precision matters.
Frequently asked questions
How do you calculate the volume inside a pipe?
Treat the pipe as a cylinder: measure the inside diameter, halve it to get the radius, then multiply the radius squared by Pi and by the length of the run. That gives you the internal volume, which you can convert to gallons or liters.
Does pipe wall thickness matter?
Yes. Volume depends on the inside diameter (ID), not the outside. Schedule 40 and Schedule 80 PVC share the same outside diameter but have different wall thicknesses, so their internal capacity is different even at the same nominal size.
Can I calculate cubic feet instead of gallons?
Yes. The calculator converts the internal volume to U.S. gallons (cubic inches divided by 231) and to cubic feet (cubic inches divided by 1728), so you get both units at once.
What is the difference between pipe volume and tank volume?
The math is the same for both, since a pipe and an upright cylindrical tank are both cylinders. The difference is proportions: pipes have small diameters over long runs, while tanks are wide and short.
Does the pipe's slope change the volume?
No. The static capacity of a pipe stays the same no matter how it's angled. Slope affects how fast liquid flows through it under gravity, which is a flow-rate question, not a volume one.
Do elbows and fittings add volume?
Slightly. Curved joints hold a bit more than a straight tube of the same length. Measuring point to point along the centerline accounts for the sweep and gives you an accurate figure for most jobs.
How many gallons of water are in a pipe?
It depends on the inside diameter and length. A full run holds about ID² × 0.0408 gallons per foot, where ID is the inside diameter in inches. So 100 feet of 3/4-inch Schedule 40 PVC (0.824-inch ID) holds about 2.8 gallons, while 100 feet of 4-inch pipe holds roughly 65 gallons. Enter your own ID and length above for the exact figure.
How many gallons per foot are in a 6-inch pipe?
About 1.47 gallons per foot for a true 6-inch inside diameter (0.0408 × 6²). 6-inch Schedule 40 pipe has a 6.065-inch inside diameter, so it holds about 1.50 gallons per foot. For comparison, a 4-inch ID holds about 0.65 gallons per foot and an 8-inch ID about 2.61.
Does PEX hold less water than copper or PVC at the same size?
Yes. Nominal size names the fitting, not the bore. At 3/4 inch, PEX has about a 0.671-inch inside diameter versus 0.785 inch for Type L copper and 0.824 inch for Schedule 40 PVC, so a PEX run holds roughly a third less water than PVC of the same nominal size. Always calculate from the actual inside diameter, not the label.
Related calculators
Sources
- Volume of a CylinderMath is FunFormula for cylinder volume (pi x radius squared x length) used to compute internal pipe capacity from inside diameter.
- NIST Handbook 44 — Appendix C, General Tables of Units of MeasurementNational Institute of Standards and Technology (NIST)Basis for the exact conversion constants: 231 cubic inches per U.S. gallon and 1,728 cubic inches per cubic foot.
- Thermoplastic Pipes — Schedule 40 DimensionsThe Engineering ToolBoxDimension table showing how outside diameter, wall thickness, and inside diameter relate — the inside diameter is what governs internal volume.
- PVC & Copper Pipe Dimension Specs (Schedule 40/80 and Type L)Petersen ProductsSource for the per-size inside diameters used in the material table: Schedule 40 and 80 PVC, and Type L/M copper tube.
- PEX Tubing Dimensions (SDR-9, ASTM F876)SupplyHouse.comAverage PEX inside diameters by nominal CTS size, reflecting the SDR-9 outside-diameter-controlled sizing of ASTM F876.