Pipe Volume Calculator
Find how many gallons a length of pipe holds.
How this calculator works
volume = π × (inside diameter ÷ 24)² × length
Use the inside diameter, not the nominal size. Nominal pipe sizes are a naming convention, not a measurement — 2 inch schedule 40 PVC actually measures 2.049 inches inside, and copper is smaller than its nominal size.
Switch the site to metric — the control is in the footer — and your inputs, your results and the tables below follow. The formula, the constants, the guidance text and the sources stay in US units on purpose: that is how the standards they come from are written, and restating them would detach each figure from the document you are meant to be able to check it against.
Where these numbers come from
- ASME B36.10M (Welded and Seamless Wrought Steel Pipe) 2022 — the difference between nominal pipe size and actual inside diameter
- NIST Special Publication 811 2008 — the US gallon as 231 cubic inches
The edition matters as much as the number. Jurisdictions adopt code revisions on their own schedule, so verify which one applies where you are building.
Worked example
With inside diameter 2 in, pipe length 100 ft, this calculator returns 16.32 gal.
Water held by common pipe runs
Open any row to load it into the calculator above — the link carries the numbers with it, so it can go straight to a supplier or a crew.
| Job | Size | Volume |
|---|---|---|
| ¾ in supply line | 0.75 in × 60 ft | 1.38 gal |
| 1 in service line | 1 in × 100 ft | 4.08 gal |
| 2 in irrigation main | 2 in × 200 ft | 32.64 gal |
| 4 in drain line | 4 in × 50 ft | 32.64 gal |
| Pool return loop | 1.5 in × 80 ft | 7.34 gal |
Use the measured inside diameter. Nominal size is a name, not a measurement — 2 in schedule 40 PVC is 2.049 in inside.
Frequently asked questions
How many gallons in 100 feet of 2 inch pipe?
About 16.3 gallons. A 4 inch pipe of the same length holds four times as much at 65 gallons, since volume scales with the square of the diameter.
Should I use nominal or inside diameter?
Inside diameter, always. Nominal pipe size is a naming convention that stopped matching reality decades ago — 2 inch schedule 40 PVC measures 2.049 inches inside, while 2 inch copper type L measures 1.985.
Why does pipe volume matter?
For flushing and chlorinating a new line, for sizing an expansion tank, for working out how long hot water takes to reach a fixture, and for knowing how much a system holds before draining it.
How much does water in a pipe weigh?
Water weighs 8.34 lb per US gallon. A 100 ft run of 4 inch pipe holds 65 gallons — about 545 lb, which matters when hanging pipe from joists.