Pipe Volume Calculator
Enter your pipe’s inner diameter and length. Get total gallons (or liters) of fluid the pipe holds when full. The calculator takes the actual inner diameter, not the nominal pipe size on the label. A 1-inch PVC pipe has an actual ID of 1.029 in. A 1-inch copper Type L has an ID of 1.025 in. A 1-inch PEX has an ID of 0.875 in, which holds 28 percent less water. The reference table covers common PVC, copper, and PEX sizes so you can look up your pipe before entering.
Results
Estimates only. Pipe volume varies with the pipe's actual inner diameter, which is usually slightly different from the labeled NPS size. The reference table covers common pipe types; for unusual materials or schedules, check the manufacturer's spec sheet for actual ID. TakeoffCalc isn't responsible for over- or under-fill in plumbing, irrigation, or chemical-dosing applications.
How to use this calculator
- 01Find your pipe's actual inner diameter. Look it up in the reference table below if you only know the nominal size.
- 02Enter the inner diameter in inches (or centimeters in metric mode).
- 03Enter the length of the pipe run in feet (or meters).
- 04Read the total gallons (liters in metric) at the top of the results panel.
- 05For mixed-material runs, calculate each material section separately and add the gallons. PEX and PVC at the same nominal size hold meaningfully different volumes.
Understanding the math
One formula for any cylindrical pipe:
V = π × (inner diameter / 2)² × length
Convert volume to gallons:
volume (cu ft) × 7.4805 = gallons (7.4805 = US liquid gallons per cubic foot, NIST)
The “inner diameter” in the formula is the actual ID of the pipe, not the nominal pipe size on the label:
Examples for 1-inch nominal pipe: PVC Schedule 40: actual ID 1.029 in Copper Type L: actual ID 1.025 in PEX: actual ID 0.875 in Same nominal size. Different actual IDs. Different volumes. PEX holds 28 percent less than PVC at the same labeled size.
Worked example: a 100-ft (30.5-m) run of pipe with an inner diameter of 1.029 inches (2.6 cm). Convert diameter to feet: 1.029 / 12 = 0.0858 ft (0.026 m). Inner radius is 0.0858 / 2 = 0.0429 ft (0.013 m). Cross-sectional area is π × 0.0429² = 0.00578 sq ft (0.000537 m²). Volume is 0.00578 × 100 = 0.578 cu ft (0.0537 m³). Gallons is 0.578 × 7.4805 ≈ 4.32 gallons (16.4 L).
Common pipe sizes (NPS to actual ID)
Common residential pipe sizes with their actual inner diameters. Enter the Inner Diameter value into the calculator. Don’t enter the NPS size: a 1-inch pipe has an actual inner diameter of around 1 inch for PVC, slightly different for copper, and quite a bit smaller for PEX.
| NPS Size | Material | Outer Diameter | Inner Diameter | Volume per 100 ft |
|---|---|---|---|---|
| 1/2 in | PVC Sch 40 | 0.840 in | 0.602 in | 1.5 gal |
| 3/4 in | PVC Sch 40 | 1.050 in | 0.804 in | 2.6 gal |
| 1 in | PVC Sch 40 | 1.315 in | 1.029 in | 4.3 gal |
| 1.5 in | PVC Sch 40 | 1.900 in | 1.610 in | 10.6 gal |
| 2 in | PVC Sch 40 | 2.375 in | 2.067 in | 17.4 gal |
| 1/2 in | Copper Type L | 0.625 in | 0.545 in | 1.2 gal |
| 3/4 in | Copper Type L | 0.875 in | 0.785 in | 2.5 gal |
| 1 in | Copper Type L | 1.125 in | 1.025 in | 4.3 gal |
| 1/2 in | PEX | 0.625 in | 0.475 in | 0.9 gal |
| 3/4 in | PEX | 0.875 in | 0.681 in | 1.9 gal |
| 1 in | PEX | 1.125 in | 0.875 in | 3.1 gal |
Frequently asked questions
How to calculate pipe volume?
Volume of a pipe is π × (inner diameter / 2)² × length. Inner diameter and length need to be in the same unit before squaring (both in feet, or both in meters). Convert cubic feet to gallons by multiplying by 7.4805. So a 100-ft run of pipe with a 1.029-inch inner diameter is π × (1.029/24)² × 100 = 0.578 cu ft, then × 7.4805 ≈ 4.32 gallons.
Or skip the math and use the calculator above. The reference table on this page covers common PVC, copper, and PEX sizes so you can look up your actual inner diameter without converting from nominal sizes by hand.
What's the difference between NPS and actual inner diameter?
Nominal Pipe Size is the label number stamped on the pipe, typically the size used to identify and sell it. Actual inner diameter is the real measurement of the inside of the pipe, which is what determines how much fluid the pipe holds. The two are usually different, sometimes by a lot. A 1-inch PVC Schedule 40 pipe has an actual inner diameter of 1.029 inches because the wall thickness is set by the schedule. A 1-inch PEX pipe has an actual ID of 0.875 inches because PEX has thicker walls relative to its NPS. Use the actual ID for any volume calculation. The NPS value alone will give a wrong answer.
Why does pipe ID differ between PVC, copper, and PEX?
Pipe materials have different wall thicknesses, and wall thickness is set by the schedule (for PVC and steel) or material standard (for copper and PEX). PVC Schedule 40 walls are sized for pressure ratings. Copper Type L walls are sized for the soldering and water-supply standard. PEX walls are thicker because the polymer needs more material to hit the same burst-pressure rating as a thinner copper wall. The result: same nominal label, three meaningfully different actual IDs. A 1-inch PEX run holds about 28 percent less water than a 1-inch PVC run of the same length.
Can I use this calculator with metric measurements?
Yes. Toggle the unit system at the top of the form to switch the inner-diameter input from inches to centimeters and the length input from feet to meters. The output flips from gallons to liters and from cubic feet to cubic meters. The math runs in imperial internally and converts at the input and output edges, so the precision stays the same in either system.
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