Pipe Volume Calculator
Calculate the water volume of a pipe in gallons and cubic feet from inside diameter and length. For plumbing, irrigation, and system fill estimates.
How this calculator works
A pipe is a cylinder, so its volume is pi times the radius squared times the length. The calculator takes the inside diameter in inches and the length in feet, and returns gallons and cubic feet.
Formula: Cubic feet = π × (inside diameter ÷ 24)² × length ft. Gallons = cubic feet × 7.48.
Worked example
A 2-inch inside-diameter pipe, 50 feet long:
- Radius in feet: 2 ÷ 24 = 0.0833 ft
- Cubic feet: π × 0.0833² × 50 ≈ 1.091 ft³
- Gallons: 1.091 × 7.48 ≈ 8.16 gallons
Reference (gallons per foot)
| Inside diameter | Gallons per foot |
|---|---|
| 1 in | 0.041 |
| 2 in | 0.163 |
| 3 in | 0.367 |
| 4 in | 0.653 |
How to use
Look up or measure the pipe’s true inside diameter, enter the total run length, and read the volume. For hot-water delivery time, divide the pipe volume by your fixture’s flow rate.
Frequently asked questions
Why use inside diameter, not the pipe's nominal size?
Nominal pipe size (like ½-inch) is a label, not the actual bore. A ½-inch copper pipe has an inside diameter closer to 0.545 inches, and PVC differs again. For accurate volume, measure or look up the true inside diameter.
What is pipe volume useful for?
Knowing the water a pipe holds matters for sizing a water heater's recovery, estimating how long it takes hot water to reach a fixture, dosing chemicals in irrigation or pools, calculating drain-down volume, and filling or flushing a system.
How many gallons are in a foot of pipe?
It depends entirely on diameter. A 2-inch pipe holds about 0.163 gallons per foot, while a 4-inch pipe holds four times that. The calculator does the math for your exact size and length.
Does length include fittings and vertical runs?
Enter the total developed length of the pipe — horizontal plus vertical runs. Fittings add a small amount of volume that's usually negligible for estimating; add it only for precise system-fill calculations.
Can I use this for a round tank or well casing?
Yes — the math is the same cylinder formula. For larger vessels measured in feet, the Tank Volume Calculator uses foot-based inputs; this one is tuned for pipe diameters in inches.
Estimates only. Verify quantities with your supplier before purchasing.