Flow Rate Calculator
Calculate volumetric and mass flow rate for pipes, pumps, and fluid systems.
Need to calculate tank capacity or partial fill volume? Try our Tank Volume Calculator.
Input
Result
Formula
Q = A × v
Understanding Flow Rate Calculations
Flow rate measures the volume or mass of fluid passing through a cross-section per unit time. It's fundamental to plumbing, HVAC, chemical processing, and hydraulic system design. Accurate flow calculations ensure proper pipe sizing, pump selection, and system efficiency.
Key Formulas
Where Q is volumetric flow rate (m³/s), A is cross-sectional area (m²), v is flow velocity (m/s), and ρ is fluid density (kg/m³).
How to Calculate Flow Rate
Frequently Asked Questions
How do I calculate flow rate?
Flow rate Q = cross-sectional area × flow velocity. For a circular pipe: Q = π × (d/2)² × v. For a rectangular duct: Q = w × h × v. Ensure all units are consistent (e.g., meters and m/s gives m³/s).
How do I calculate the cross-sectional area of a pipe?
For a circular pipe: A = π × r² = π × (d/2)². Use the inner diameter (not outer) for flow calculations. For a rectangular duct: A = width × height. Always use internal dimensions.
What is GPM?
GPM stands for Gallons Per Minute — a common unit for volumetric flow rate in the US. 1 GPM = 3.7854 L/min = 0.06309 L/s = 0.2271 m³/h. Typical residential water flow is 6–12 GPM.
How do I convert L/min to GPM?
Divide L/min by 3.7854 to get GPM. For example, 20 L/min ÷ 3.7854 = 5.28 GPM. Conversely, multiply GPM by 3.7854 to get L/min.
What is the difference between volumetric and mass flow rate?
Volumetric flow rate (Q) measures volume per time (L/min, GPM, m³/h). Mass flow rate (ṁ) measures mass per time (kg/s, lb/min). They're related by density: ṁ = ρ × Q. For water (ρ ≈ 1000 kg/m³), 1 m³/s = 1000 kg/s.