Flow Rate Calculator
Calculate volumetric flow rate using either volume over time or cross-sectional area times velocity.
How to Use This Calculator
Choose a method
Select Area × Velocity (for pipes/ducts) or Volume ÷ Time (for batch measurements).
Enter inputs
Use SI units: meters (m), seconds (s), and cubic meters (m³) for best results.
Calculate and interpret
The result is Q in m³/s. Convert as needed to L/s, L/min, or GPM.
Formula
Q = V / t or Q = A · v
Where: Q = flow rate (m³/s), V = volume (m³), t = time (s), A = cross-sectional area (m²), v = average velocity (m/s).
Example: Circular pipe with diameter 0.1 m, velocity 2 m/s → A = π(0.05)² = 0.00785 m², so Q = 0.00785 × 2 = 0.0157 m³/s.
About Flow Rate Calculator
This tool helps engineers, students, and technicians compute volumetric flow in pipes, ducts, and open channels using standard relationships.
Common Applications
- HVAC air flow estimation
- Water and wastewater pipe sizing
- Process engineering flow balancing
Tips
- Use consistent units; convert diameters to meters.
- For non-circular sections, compute the actual area.
- Velocity should be average, not peak.
Frequently Asked Questions
What units does the calculator use?
Inputs are in SI units (m, s). The output is m³/s.
How do I get L/s or GPM?
1 m³/s = 1000 L/s. 1 m³/s ≈ 15850.3 GPM.
Does pipe roughness matter?
Not for Q directly. Roughness affects head loss, not the definition of flow rate.