Pipe Volume Calculator
Fluid volume — gallons, liters, ft³ — for any standard pipe size and length. Also outputs water weight for system loading.
Volume
—
— L
Volume in ft³
—
ft³
Per foot of pipe
—
gal/ft
Fluid weight
—
lb
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How fluid volume in a pipe is calculated
A pipe is a cylinder. The internal volume is the inside-diameter cross-section area times the length. The trick is knowing your inside diameter — it's not the nominal pipe size. NPS 2" is 2.067" ID at Sch 40, 1.939" at Sch 80, 1.687" at Sch 160. Always pull the actual ID from the pipe schedule chart.
Volume = (π / 4) × ID² × Length
Gallons = (cubic inches) / 231
Liters = (cubic inches) × 0.01639
ft³ = (cubic inches) / 1728
Worked example: 100 ft of 4" SCH 40 water line
4" SCH 40 has an ID of 4.026". Volume per foot: π/4 × 4.026² × 12 = 152.8 in³/ft → 0.661 gal/ft → 5.50 lb/ft (water). Over 100 feet: 66.1 gallons and 551 lb of fluid weight. Useful when sizing pipe hangers — the water alone doubles the empty pipe weight.
Common gallon-per-foot values (water, Sch 40)
| NPS | ID (in) | gal / ft | L / m |
|---|---|---|---|
| 1/2" | 0.622 | 0.0158 | 0.196 |
| 3/4" | 0.824 | 0.0277 | 0.344 |
| 1" | 1.049 | 0.0449 | 0.558 |
| 1-1/4" | 1.380 | 0.0777 | 0.966 |
| 1-1/2" | 1.610 | 0.106 | 1.314 |
| 2" | 2.067 | 0.174 | 2.162 |
| 2-1/2" | 2.469 | 0.249 | 3.087 |
| 3" | 3.068 | 0.384 | 4.770 |
| 4" | 4.026 | 0.661 | 8.214 |
| 6" | 6.065 | 1.501 | 18.65 |
| 8" | 7.981 | 2.598 | 32.28 |
| 10" | 10.020 | 4.096 | 50.89 |
| 12" | 11.938 | 5.815 | 72.24 |
Frequently asked questions
Volume formula?
V = (π/4) × ID² × L. Convert in³ to gallons by dividing by 231.
Gallons in 100 ft of 2" SCH 40?
~17.4 gallons of water.
How much does water weigh?
8.34 lb/gal at 60°F. About 62.4 lb/ft³.
GPM from pipe size?
GPM = velocity (ft/s) × area (ft²) × 449. Reasonable design velocities: water 5–8 ft/s, fuel oil 3–6 ft/s.