Flow Rate Calculator


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Flow rate calculator is an online tool that is used to calculate the rate of flow of water in an area. It can be used to calculate the flow rate in your kitchen sink pipe, gardening hose, water pipe, and water tank, etc. This flow calculator can process the water flow calculation in circular, trapezoidal, and rectangular areas as well. In this post, we will discuss what volumetric flow rate is, how to calculate the flow rate, and flow rate formula.

How to use our calculator?

You can calculate the volumetric flow rate in rectangular, circular, or trapezoidal area. To calculate the flow rate using the above calculator:

  • Select the type of calculation by choosing from the given options. For each selection, you will be asked to enter a different type of values due to varying formulas for each. For example, if you select a circle, you should enter pipe diameter and velocity.
  • Enter the required values in the corresponding input boxes.
  • You can choose the unit from given options if your measurements are in different units.
  • Press the calculate button after entering the values.

It will instantly show you the flow rate of the fluid. You can also use our blood pressure calculator to check the flow rate of your blood.

What is flow rate?

You will definitely consider the idea of the Volume Flow Rate when we talk about the flow rate. The flow rate can be defined as the volume of a given fluid, which crosses a given cross-section area by the unit of time. The symbol Q is used to represent the flow rate. The flow rate unit is cubic meter per second \(m^3/s\).

Flow Rate Formula

The volumetric flow rate equation is as follow:

Flow rate = \(\dfrac{V}{t}\)

In this equation:

\(V\) represents the volume of fluid, and

\(t\) refers to the time.

How to calculate Flow rate?

To calculate the flow rate of a fluid, let’s first go through some of the basic formulations of the volumetric flow rate. Above formula for flow rate can also be written as:

Volumetric flow rate = \(A \times v\)

In this equation:

\(A\) represents the cross-sectional area, and

\(v\) represents the volume of fluid.

Alright! Don’t get confused by multiple equations for flow rate. We will explain it in detail. The formula for volume flow rate can be written in this form too. The volume of a portion of the fluid in a channel can first be measured as:

Volume = \(A \times l\)


\(l\) is the width of a particular part of the fluid

\(A\) is a transverse area of the fluid.

The formula for cylinder volume can be used if the pipe in which fluid is flowing is circular. We can obtain the volume flow rate equation by placing the above equation in the flow rate formula:

Flow rate = \(\dfrac{V}{t} = A \times \dfrac{l}{t}\)

Since \(\dfrac{l}{t}\) is the time-divided volume length, you can see it is just the speed of the fluid. In other words, it is the flow velocity. So, we can write the flow rate formula as:

Volumetric flow rate = \(A \times v\)

Most of the pipes are cylindrical so the flow rate equation can be written as:

Volumetric flow rate for cylindrical pipe = \(\Pi \times \Big(\dfrac{d}{2}\Big)^2 \times v\) 

In this equation:

\(d\) refers to the diameter of the pipe.

Example of calculating flow rate:

Suppose we have a pipe with a radius of 0.3 meters, which is attached to a cylindrical tank of water. The diameter of the tank is 4 meters and the height is 2 meters. Calculate the flow rate of water through this pipe if the water tank has to be emptied in one hour.


Follow these steps to calculate the volumetric flow rate:

Step 1: Calculate the volume of water in the water tank. Use diameter to get the radius.

Volume of water in tank = \(\Pi \times \Big(\dfrac{d}{2}\Big)^2 \times h = 58.9 m^3\)

= \(\Pi \times \Big(\dfrac{4}{2})^2 \times 2m = 25.13 m^3\)

Step 2: Now, calculate the flow rate required to empty the tank in an hour.

\(Q = \dfrac{V}{t} = \dfrac{25.13}{3600} = 0.0069 m^3/s\)

Step 3: Calculate the area of the pipe.

\(A = \Pi r^2 = 3.1415 × 0.3^2 = 0.94 m^2\)

Step 4: By using the flow rate equation, we can calculate the flow rate of water.

\(V = \dfrac{Q}{A} = \dfrac{0.0069}{0.94} = 0.0073 m/s\)