Volumetric Flow Rate & Pipe Discharge Calculator
Calculate water pump discharge rates, irrigation line capacity, plumbing flow sizing, and chemical piping throughput instantly.
How it works
Applies the continuity equation Q = v × A. If pipe diameter is entered, cross-sectional area is calculated as A = π × D² / 4 and multiplied by mean velocity.
Formula
Q = v × A = v × (π × D² / 4), 1 m³/s = 1,000 L/s = 60,000 LPM
Calculates liquid volume passing through a cross-section per unit time by multiplying fluid velocity by internal pipe area.
| Symbol | Variable | Unit | Description |
|---|---|---|---|
| v | Average fluid flow velocity | m/s | |
| A | Internal cross-sectional flow area | m² | |
| D | Internal pipe diameter | m | |
| Q | Volumetric flow rate | m³/s |
Worked example
2.0 m/s water velocity in a 50mm (0.05m) pipeline
- Velocity:
- 2.0 m/s
- Diameter:
- 0.05 m (50 mm)
Area A = π × (0.05)² / 4 = 0.001963 m². Q = 2.0 × 0.001963 = 0.003927 m³/s = 3.927 L/s = 235.6 Litres/minute (14.14 m³/hr).
Limitations
Does not calculate friction head loss or pressure drop along the pipe length.
Frequently asked questions
What is a good recommended water velocity for residential plumbing?
Standard plumbing codes recommend water velocities between 1.0 m/s and 2.4 m/s (approx. 4 to 8 ft/s). Speeds below 1 m/s cause sediment deposition; speeds above 2.5 m/s cause pipe erosion and noisy water hammer.
How does pipe diameter affect flow rate for a fixed velocity?
Flow capacity scales with the square of the diameter ($D^2$). Doubling the pipe diameter quadruples ($2^2 = 4\times$) the flow capacity at the same velocity.
How do I convert LPM to GPM (US Gallons per Minute)?
Divide Litres per Minute by 3.78541. For example, 235.6 LPM equals approx. 62.24 US GPM.
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Last reviewed: 2026-08-22.