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Flow Rate Calculator
Calculate volumetric flow from cross-sectional area and fluid velocity, solve for area or velocity, or estimate how long a tank takes to fill. Choose common metric or US customary units.
How do I calculate flow rate?
For steady flow through a section, volumetric flow rate Q equals cross-sectional area A multiplied by average velocity v: Q = A × v. To estimate filling time, divide container volume by flow rate. Real systems can vary with pressure, friction, fittings, fluid properties and changing levels.
Frequently asked questions
How do I calculate flow rate?
For steady flow through a section, volumetric flow rate Q equals cross-sectional area A multiplied by average velocity v: Q = A × v. To estimate filling time, divide container volume by flow rate. Real systems can vary with pressure, friction, fittings, fluid properties and changing levels.
Are my flow values uploaded?
No. Calculations run in this browser. Values you enter are not uploaded or saved by this tool.
What is the flow rate for a 2 m² section moving at 3 m/s?
Using Q = A × v, 2 m² × 3 m/s = 6 m³/s. This is an ideal volumetric estimate for the entered average velocity.
How do I calculate pipe flow rate?
Multiply the pipe cross-sectional area by average fluid velocity. For a circular pipe, area is π times the internal diameter squared divided by four; use the inside diameter, not the outside diameter.
How do I estimate how long a tank takes to fill?
Divide the tank volume by the flow rate, using compatible volume and time units. The estimate assumes flow remains constant and the tank does not overflow or lose fluid.
Does this calculate pressure loss or pump size?
No. It only relates area, average velocity and volumetric flow, or estimates fill duration. Pressure loss and pump selection also depend on fluid, pipe length and roughness, fittings, elevation and system operating conditions.