Flow Rate Calculator
Volumetric flow from pipe area and average velocity.
Calculator
No signup required. Results are indicative—verify for your standards.
Flow rate: 0.0628 m³/s · 3770 L/min
Formula
Q = A × v, where A = π × (D/2)² for circular duct/pipe, v is average axial velocity.
Example calculation
200 mm ID, v = 2 m/s: A ≈ 0.0314 m², Q ≈ 0.0628 m³/s.
Engineering notes
Velocity profiles are not flat; Q is based on average v. For compressible flow at high ΔP, use corrected density and Mach considerations.
When to use this calculator
- Pipe sizing — verify that a proposed pipe bore gives acceptable velocity for the design flow rate
- Flow meter selection — confirm the flow range matches the meter's rangeability
- Mass flow estimation — multiply volumetric flow by fluid density for mass flow calculations
- Velocity check — ensure liquid lines stay within 1.5–3 m/s and suction lines under 1 m/s to avoid erosion and cavitation
- HVAC and ventilation — calculate air volume flow in circular ducts from duct diameter and measured velocity
Frequently asked questions
- What is the recommended velocity for water in industrial pipes?
- For water in carbon steel pipes: discharge lines 1.5–3 m/s, suction lines 0.5–1.5 m/s. For pump suction, keeping velocity below 1 m/s reduces NPSHa loss and helps prevent cavitation. For slurries, minimum velocity must exceed the settling velocity of solids (typically 1.5–3 m/s depending on particle size and density).
- How do I find flow rate if I know pressure drop but not velocity?
- Use the pressure drop calculator (Darcy-Weisbach) in reverse: rearrange to find velocity from ΔP, then multiply by pipe area to get flow rate. Alternatively, for orifice meters and venturis, use the differential pressure and discharge coefficient to derive flow rate from ΔP across the meter.
- Can I use this calculator for gas or air flows?
- Yes, for incompressible or low-pressure gas flows (Mach < 0.3), Q = A × v is a reasonable approximation. However, gas density changes with pressure and temperature, so the volumetric flow at operating conditions differs from the flow at standard conditions (Nm³/h or SCFM). Apply ideal gas law corrections when comparing flows at different pressures.
- What is the difference between volumetric flow and mass flow?
- Volumetric flow (Q, m³/s or m³/h) measures the volume of fluid passing a cross-section per unit time. Mass flow (ṁ, kg/s or kg/h) = Q × ρ, where ρ is fluid density. Mass flow is conserved regardless of pressure and temperature changes, making it preferred for process control and energy balance calculations. Volumetric flow is more convenient for pipe sizing.