Volumetric Flow Rate Calculator
Given the average flow velocity inside a pipe and the pipe diameter, this calculator finds the volumetric flow rate - the amount of fluid passing through per second. Results are shown in m³/s, L/s, and m³/h for convenience. This is the reverse of the Pipe Flow Velocity Calculator.
Calculate Volumetric Flow Rate (Q = V × A)
Results
The Formula Explained
Flow rate is simply velocity times the area the fluid flows through. For a circular pipe:
Q = V × A = V × π × D² / 4 - Q - volumetric flow rate (m³/s)
- V - average flow velocity (m/s)
- A - pipe cross-sectional area (m²) = π × D² / 4
- D - pipe internal diameter (m)
If you know Q and want to find V, use the Pipe Flow Velocity Calculator - it's the inverse of this tool.
Worked Example
Water flows at 2.5 m/s through a 200 mm (0.2 m) diameter pipe.
A = π × (0.2)² / 4 = 0.03142 m²
Q = 2.5 × 0.03142
Q = 0.07854 m³/s = 78.54 L/s = 282.7 m³/h
Common Flow Rate Conversions
Frequently Asked Questions
Does flow rate stay constant along a pipe?
Yes - for an incompressible fluid (liquids) in a closed pipe, flow rate Q is constant along the pipe length (continuity equation). Velocity changes only when the pipe diameter changes. At a constriction, velocity increases; at an expansion, velocity decreases - but Q stays the same.
Why does velocity matter more than flow rate for friction calculations?
The Darcy-Weisbach equation uses velocity (V) in the dynamic pressure term (ρV²/2). Reynolds number also uses velocity. Flow rate Q is useful for process design, but friction calculations work in velocity. That's why engineers always convert between Q and V depending on what's known.
Related Tools
⚡ Pipe Flow Velocity Calculator
The reverse: find velocity from flow rate and diameter.
🌊 Reynolds Number Calculator
Use velocity from this tool to calculate Reynolds number next.
⚙️ Pump Power Calculator
Use Q from this tool as input to pump power sizing.
📊 Moody Chart Calculator
After finding velocity → Re → friction factor with the Moody Chart.