Volumetric Flow Rate Calculator
Enter a cross-sectional area and a flow velocity to get the volumetric flow rate in cubic metres per second — and the same flow in litres per second.
Two units at once
Enter the area and velocity and the calculator returns the flow rate (Q = A·v) in cubic metres per second and in litres per second together.
Use SI units
Area in square metres and velocity in metres per second give the flow in m³/s — convert a pipe diameter to area with π × radius² first.
What is volumetric flow rate?
Volume of fluid per second
The volumetric flow rate calculator turns two measurements — the cross-sectional area in square metres and the flow velocity in metres per second — into the volume of fluid passing a point each second. Volumetric flow rate is how much fluid moves through a pipe, duct, or channel per unit of time, and it is the number behind sizing a pump, a water main, a ventilation duct, or an irrigation line. Multiply the area the fluid flows through by how fast it travels and you get the flow rate in cubic metres per second, which the calculator also shows in the more everyday unit of litres per second.
Enter a cross-sectional area in square metres and a velocity in metres per second to get the volumetric flow rate in m³/s and L/s instantly.
Volumetric flow rate is the cross-sectional area multiplied by the flow velocity, and litres per second is simply that result times 1000.
Q = A × vSuppose fluid flows at 2 m/s through a pipe with a cross-sectional area of 0.01 m². Multiply the area by the velocity: 0.01 × 2 = 0.02 m³/s. Because one cubic metre is 1000 litres, that same flow is 0.02 × 1000 = 20 litres per second. Keep the area in square metres and the velocity in metres per second and the flow comes back in cubic metres per second, with the litres-per-second figure alongside it.
The formula is exact, but a couple of practical points are worth keeping in mind.
Average velocity and consistent units
This calculator uses the average velocity across the whole cross-section. Real flow in a pipe is faster in the centre and slower near the walls, so use the mean velocity, not the peak. Keep your units consistent — square metres for area and metres per second for velocity — or the result will be wrong: convert a pipe diameter to area with π × radius² before you start, and the flow rate will be assumed incompressible (constant density).