What Is a Flow Rate Calculator?
A flow rate calculator finds the volumetric flow rate of a fluid — how much volume passes a point per unit time. It can compute flow rate from a volume and a time, or from a pipe's cross-sectional area and the fluid's velocity. Flow rate is essential in plumbing, engineering, and fluid dynamics. Enter your known values and the calculator returns the flow rate, or solves for area or velocity.
How to Use the Calculator
- Choose your method — volume and time, or area and velocity.
- Enter the known values.
- Calculate — see the flow rate.
Flow Rate Formulas
From volume and time:
Flow Rate = Volume ÷ Time
From pipe area and velocity:
Q = A × v
where Q is the flow rate, A is the cross-sectional area, and v is the velocity. For a round pipe, A = π × radius².
Common Flow Rate Units
| Unit | Use |
|---|---|
| Gallons per minute (GPM) | Plumbing, pumps |
| Liters per minute (LPM) | Metric fluid systems |
| Cubic meters per second | Engineering, large flows |
| Cubic feet per second (CFS) | Rivers, large pipes |
The Continuity Principle
For an incompressible fluid in a closed pipe, the flow rate is constant: where the pipe narrows, the velocity increases, and where it widens, the velocity decreases (A × v stays the same). This is why a nozzle speeds up water at the end of a hose.
Frequently Asked Questions
How do you calculate flow rate?
Divide volume by time, or multiply the pipe's cross-sectional area by the fluid velocity (Q = A × v). The calculator supports both methods.
What is volumetric flow rate?
It is the volume of fluid passing a point per unit time, such as gallons per minute or cubic meters per second.
How does pipe size affect flow?
For a constant flow rate, a narrower pipe increases velocity and a wider pipe decreases it, following the continuity equation A × v = constant.
What is the area of a round pipe?
The cross-sectional area is π × radius². Use this for A in the flow rate formula Q = A × v.
Is this flow rate calculator free?
Yes — it is completely free, requires no signup, and solves for flow, area, or velocity.