Quick answer: gallons = 0.0408 × inside diameter (in)² × length (ft). A 2 in Schedule 40 pipe holds about 0.174 gallons per foot.
How to calculate pipe volume
- Find the inside diameter (ID). It is printed in pipe charts and on spec sheets; it is not the nominal size.
- Measure the length of the run in feet, including fittings if you want to be precise.
- Volume (cu ft) = π × (ID ÷ 24)² × length, with the ID in inches.
- Gallons = cubic feet × 7.4805.
Gallons = π ÷ 4 × ID² ÷ 144 × L × 7.4805 = 0.0408 × ID² × L
The 0.0408 is π ÷ 4 ÷ 144 × 7.4805: it combines the circle area, square inches to square feet, and cubic feet to US gallons (231 cubic inches each).
Gallons per foot of Schedule 40 pipe
| Nominal size | Inside diameter | Gallons per ft | Gallons per 100 ft | Liters per m |
|---|---|---|---|---|
| ½ in | 0.622 in | 0.0158 | 1.58 | 0.196 |
| ¾ in | 0.824 in | 0.0277 | 2.77 | 0.344 |
| 1 in | 1.049 in | 0.0449 | 4.49 | 0.558 |
| 1¼ in | 1.380 in | 0.0777 | 7.77 | 0.965 |
| 1½ in | 1.610 in | 0.1058 | 10.58 | 1.313 |
| 2 in | 2.067 in | 0.1743 | 17.43 | 2.165 |
| 3 in | 3.068 in | 0.3840 | 38.40 | 4.769 |
| 4 in | 4.026 in | 0.6613 | 66.13 | 8.213 |
| 6 in | 6.065 in | 1.5008 | 150.08 | 18.639 |
The inside diameters are the standard Schedule 40 dimensions (ASME B36.10, also used for Schedule 40 PVC under ASTM D1785). Copper, PEX and Schedule 80 pipe have different inside diameters, so enter the ID from your pipe’s chart.
Worked examples
Flushing a water line
250 ft of 1 in Schedule 40: 250 × 0.0449 = 11.2 gallons to fill the line once.
Several runs
80 ft of 2 in plus 40 ft of ¾ in: 80 × 0.1743 + 40 × 0.0277 = 13.94 + 1.11 = 15.1 gallons. Add each run to the system total.
- Tanks and pools: try the pool volume calculator. For any other shape, use the cubic feet calculator.
Frequently asked questions
How do I calculate the volume of a pipe?
Volume = π × (inside diameter ÷ 2)² × length. With the diameter in inches and the length in feet: gallons = 0.0408 × ID² × length. A 2 in Schedule 40 pipe (2.067 in inside) 100 ft long holds about 17.4 gallons.
Should I use the nominal or the inside diameter?
The inside diameter. Nominal pipe sizes are names, not measurements: a “2 inch” Schedule 40 pipe is 2.067 in inside and 2.375 in outside. Using the nominal size can be off by several percent.
How many gallons per foot of pipe?
For Schedule 40 steel or PVC pipe: ½ in 0.016, ¾ in 0.028, 1 in 0.045, 1½ in 0.106, 2 in 0.174, 3 in 0.384, 4 in 0.661 and 6 in 1.50 gallons per foot. See the table on this page.
Why would I need the volume of a pipe?
For flushing and disinfecting a water line, sizing a glycol or antifreeze fill, working out how much water sits in a well line, or how long hot water takes to reach a tap.
How much does the water in a pipe weigh?
About 8.34 lb per US gallon. 100 ft of 4 in Schedule 40 pipe holds about 66 gallons, which is about 550 lb of water.
What is the hollow-cylinder option for?
It gives the volume of the pipe wall itself, from the outside and inside diameters. That is useful for the weight of the pipe material or for concrete-filled tubes. For the water inside, use the Pipe shape.
Is this pipe volume calculator free to use online?
Yes. The CalcWall Pipe Volume Calculator is completely free and works online in any browser, on a phone, tablet or computer. There is nothing to download and no account to create, and the math runs right in your browser, so results appear as you type.