Water Pipe Flow Calculator

About the Water Pipe Flow Calculator

Calculates the volumetric flow rate through a pipe from its internal diameter and the water velocity.

How to use this calculator

1. Enter the pipe's diameter or radius so the calculator can find the cross-sectional area.
2. Enter the water velocity, usually in meters per second or feet per second.
3. Check the calculated flow rate, which is the volume of water passing through each second.
4. Use the result to compare pipe sizes, speeds, or system capacity.

The formula explained

The formula \(Q = A v\) computes volumetric flow rate, where \(Q\) is the amount of fluid passing through the pipe per unit time, \(A\) is the pipe's cross-sectional area, and \(v\) is the flow velocity. If the pipe is full and the speed is steady, multiplying area by velocity gives the flow rate.

• Q = volumetric flow rate
• A = cross-sectional area of the pipe
• v = water velocity

Step by step method

1. Find the pipe's cross-sectional area using the radius or diameter, with \(A = \\pi r^2\).
2. Multiply the area by the water velocity using \(Q = A v\).
3. Write the final answer in volume per time, such as \(m^3/s\) or \(L/s\).

Worked example

Problem. A pipe has a radius of \(0.10\) m and the water moves at \(2.5\) m/s. What is the flow rate?

1. First find the area, \(A = \\pi (0.10)^2 = 0.0314\) m\(^2\).
2. Then multiply by the velocity, \(Q = 0.0314 \\times 2.5 = 0.0785\) m\(^3\)/s.
3. So the pipe flow rate is \(0.0785\) m\(^3\)/s.

Tips and common mistakes

• Make sure the radius and velocity use consistent units, because the flow rate depends on both.
• If you are given diameter instead of radius, divide by \(2\) before finding the area.

Frequently asked questions