Pipe Volume Calculator
Calculate the volume of water or fluid inside a pipe by entering diameter and length.
Supports inches, feet, centimeters, and meters.
Pipe volume is the total internal capacity of a cylindrical pipe — the amount of fluid it can hold when completely filled. Flow rate is how much fluid passes a fixed point per unit of time. Both calculations are essential for plumbing design, HVAC systems, irrigation, and industrial piping.
Volume of a cylinder (pipe): V = π × r² × L
Where:
- V: internal volume (liters, gallons, or cubic meters)
- π: pi, approximately 3.14159
- r: internal radius of the pipe (half the internal diameter)
- L: length of the pipe
Equivalently using diameter: V = π × (D/2)² × L = (π × D² × L) ÷ 4
Critical note: Always use the internal diameter (ID), not the external diameter. Pipe wall thickness reduces the flow bore. For example, 1-inch nominal pipe has an actual ID of about 1.049 inches in Schedule 40.
Flow rate formula: Q = A × v
Where:
- Q: volumetric flow rate (m³/s or GPM)
- A: cross-sectional area of the pipe interior = π × r²
- v: average fluid velocity (m/s or ft/s)
Fill time given flow rate: Fill Time = Volume ÷ Flow Rate
Unit conversion reference:
- 1 cubic meter = 1,000 liters = 264.17 US gallons
- 1 US gallon = 3.785 liters
- 1 GPM = 0.0631 liters/second
Worked example: A 2-inch Schedule 40 steel pipe (ID = 2.067 inches = 0.0525 m) runs 30 meters in length. Water flows at 1.5 m/s.
- Cross-section area: π × (0.0525/2)² = π × 0.000689 = 0.002165 m²
- Pipe volume: 0.002165 × 30 = 0.0650 m³ = 65.0 liters
- Flow rate: Q = 0.002165 × 1.5 = 0.00325 m³/s = 3.25 liters/second = 51.5 GPM
- Time to fill: 65.0 ÷ 3.25 = 20 seconds
Typical pipe flow velocities by application:
- Domestic cold water: 0.5–1.5 m/s
- Domestic hot water: 0.3–1.0 m/s
- Industrial process lines: 1.5–3.0 m/s
- Fire suppression mains: 2.0–4.5 m/s
Higher velocities cause noise, erosion, and water hammer — always verify against system specifications.