What is the flow rate formula?

Volumetric flow rate is Q = A × v, where A is the cross-sectional area of the flow channel and v is the mean fluid velocity perpendicular to that area. Rearranged: v = Q / A and A = Q / v.

What units does this calculator support?

Flow rate: m³/s, L/s, L/min, m³/h, GPM, CFM. Area: m², cm², mm², ft², in². Velocity: m/s, cm/s, ft/s, km/h, mph. Pick any combination — the tool converts automatically.

Does this assume circular pipes?

No. The formula Q = A × v works for any cross-section shape. For a circular pipe just enter the pre-calculated area, or use A = π r². The calculator includes a circular-pipe helper below the main inputs.

What is the difference between volumetric and mass flow rate?

Volumetric flow rate (Q) is volume per unit time. Mass flow rate (ṁ) adds fluid density: ṁ = ρ × Q. This calculator covers volumetric flow only.

Is this valid for compressible fluids like gases?

Q = A × v gives the volumetric flow rate at the local conditions. For compressible gases, properties change with pressure and temperature, so this result represents local volumetric flow; you would need to separately account for density changes for mass flow.

Flow Rate Calculator

Name: Flow Rate Calculator
Availability: InStock
Author: Nham Vu

Solve Q = A × v: enter any two of volumetric flow rate, cross-sectional area, and fluid velocity to calculate the third.

Flow Rate Calculator

Solve for

Flow Rate (Q)

Cross-Sectional Area (A)

Fluid Velocity (v)

Circular Pipe Area Helper

Pipe Diameter

Unit

Select what to solve for and enter two known values, then click Calculate.

Summary

Solve Q = A × v: enter any two of volumetric flow rate, cross-sectional area, and fluid velocity to calculate the third.

How it works

Select which variable you want to solve for: flow rate (Q), area (A), or velocity (v).
Enter the two known values with their units.
The tool applies Q = A × v (or its rearrangements A = Q / v, v = Q / A).
The result is shown in the chosen output unit with a full conversion table.

Use cases

Size a pump or pipe for a required flow rate.
Determine fluid velocity in a duct or pipe of known cross-section.
Calculate how much area is needed to achieve a target velocity.
Verify HVAC duct airflow from measured velocity readings.
Design irrigation channels or drainage systems.
Check firefighting hose flow capacity.
Convert between m³/s, L/s, GPM, and CFM quickly.
Solve textbook fluid-mechanics problems step by step.

Frequently Asked Questions

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Last updated: 2026-05-23 · Reviewed by Nham Vu