Pipe Volume Calculator
Work out how much water a pipe holds. Pick the material and nominal size, or enter your own inside diameter, add the run length, and the calculator returns the volume in US gallons, litres and cubic feet, the gallons per foot, the weight of the water and, if you enter a flow rate, how long the pipe takes to fill.
Enter values to calculate
Pipe volumeFree download
Get the printable pipe flow chart
Schedule 40 pipe sizes, water flow in GPM and LPM at four design velocities, and recommended velocities by application. One PDF, made to pin above the bench.
How It Works
A pipe is a cylinder, so the water it holds is the area of the bore times the length. The figure that needs care is the diameter: it must be the inside diameter, which for a standard pipe is set by its schedule or type, not by the nominal size printed on it.
Pipe Volume Formula
V = π × (d / 2)² × L
Where V is the volume, d is the inside diameter and L is the length, all in the same units. Metres in gives cubic metres out; multiply by 1,000 for litres.
Gallons = 0.0408 × d² × L
The US shortcut, with d in inches and L in feet: π/4 × 12 inches per foot ÷ 231 cubic inches per US gallon = 0.0408. In metric, litres = 0.0007854 × d² × L with d in mm and L in metres.
Worked Example
100 feet of 2" Schedule 40 steel pipe (inside diameter 2.067 in):
- • Gallons per foot = 0.0408 × 2.067² = 0.1743 gal/ft
- • Volume = 0.1743 × 100 = 17.43 US gallons (66.0 litres)
- • Water weight = 17.43 gal × 8.33 lb/gal ≈ 145.2 lb
- • Fill time at 10 GPM = 17.43 ÷ 10 = 1.7 minutes
Gallons per Foot of Pipe by Size
Water held by one foot and one metre of pipe, from the published inside diameters. Schedule 40 PVC has a slightly smaller average bore than Schedule 40 steel (2.049 in against 2.067 in at 2"), so choose PVC in the calculator for its figures.
| Schedule 40 steel | Type L copper | |||||
|---|---|---|---|---|---|---|
| Nominal size | ID (in) | gal/ft | L/m | ID (in) | gal/ft | L/m |
| 1/2" | 0.622 | 0.0158 | 0.196 | 0.545 | 0.0121 | 0.151 |
| 3/4" | 0.824 | 0.0277 | 0.344 | 0.785 | 0.0251 | 0.312 |
| 1" | 1.049 | 0.0449 | 0.558 | 1.025 | 0.0429 | 0.532 |
| 1-1/4" | 1.380 | 0.0777 | 0.965 | 1.265 | 0.0653 | 0.811 |
| 1-1/2" | 1.610 | 0.1058 | 1.313 | 1.505 | 0.0924 | 1.148 |
| 2" | 2.067 | 0.1743 | 2.165 | 1.985 | 0.1608 | 1.997 |
| 2-1/2" | 2.469 | 0.2487 | 3.089 | 2.465 | 0.2479 | 3.079 |
| 3" | 3.068 | 0.3840 | 4.769 | 2.945 | 0.3539 | 4.395 |
| 4" | 4.026 | 0.6613 | 8.213 | 3.905 | 0.6222 | 7.727 |
| 6" | 6.065 | 1.5008 | 18.639 | 5.845 | 1.3939 | 17.311 |
| 8" | 7.981 | 2.5988 | 32.275 | 7.725 | 2.4348 | 30.238 |
| 10" | 10.020 | 4.0963 | 50.874 | 9.625 | 3.7797 | 46.942 |
| 12" | 11.938 | 5.8146 | 72.214 | 11.565 | 5.4570 | 67.772 |
For any length, multiply gallons per foot by the run length in feet. Fittings add a little volume that is usually ignored.
Why the Inside Diameter Matters
Volume scales with the square of the bore, so small differences add up. 1" Schedule 40 steel (1.049 in bore) holds 0.0449 gal/ft, while 1" Type L copper (1.025 in) holds 0.0429 gal/ft, about 5% less. Using the nominal 1.000 in would give 0.0408 gal/ft and understate the steel pipe by 9%. The calculator uses the published inside diameter for every size.
FAQ
Answers to common questions about pipe volume.
Frequently Asked Questions
How do I calculate the volume of water in a pipe?
Multiply the area of the bore by the length: V = π × (d/2)² × L, using the inside diameter. In US units, gallons = 0.0408 × d² × L with d in inches and L in feet, so 100 feet of 2" Schedule 40 pipe (2.067 in bore) holds 17.43 gallons.
How many gallons per foot are in a 2 inch pipe?
2" Schedule 40 steel holds 0.1743 US gallons per foot (2.165 litres per metre). 2" Schedule 40 PVC, with a 2.049 in average bore, holds 0.1712 gallons per foot, and 2" Type L copper, with a 1.985 in bore, holds 0.1608.
Should I use the nominal size or the inside diameter?
Always the inside diameter. The nominal size is a name: 1/2" Schedule 40 steel pipe has a 0.622 in bore and 1/2" Type L copper 0.545 in. The calculator looks up the published inside diameter when you pick a standard size.
How much does the water in a pipe weigh?
Water weighs about 8.33 lb per US gallon (998 kg/m³ at 20 °C). 100 feet of 2" Schedule 40 pipe holds 17.43 gallons, which weighs about 145 lb, before the weight of the pipe itself.
How long does it take to fill or flush a pipe?
Divide the pipe volume by the flow rate: 17.43 gallons at 10 GPM takes 1.7 minutes. Enter a flow rate in the calculator to get the time for your pipe. Flushing and disinfection procedures often call for several pipe volumes, so check the requirement that applies to your job.
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