Fluid Flow Rate Calculator

About the Fluid Flow Rate Calculator

Calculates volumetric flow rate from pipe diameter and fluid velocity, in litres per second and cubic metres per hour.

How to use this calculator

1. Enter the flow velocity, \(v\), in units like \(\text{m/s}\).
2. Enter the cross-sectional area, \(A\), in units like \(\text{m}^2\).
3. The calculator multiplies area by velocity to find flow rate, \(Q\).
4. Check that your units match, because \(\text{m}^2 \cdot \text{m/s} = \text{m}^3/\text{s}\).

The formula explained

The formula \(Q = A v\) computes volumetric flow rate, which is the volume of fluid passing through a cross section each second. If either the area or the velocity changes, the flow rate changes too.

• Q = volumetric flow rate, usually in \(\text{m}^3/\text{s}\) or \(\text{L/s}\)
• A = cross-sectional area, usually in \(\text{m}^2\)
• v = fluid velocity, usually in \(\text{m/s}\)

Step by step method

1. Write down the area \(A\) and the velocity \(v\).
2. Multiply them using \(Q = A v\).
3. Simplify the units to get a volume per time unit.
4. If needed, convert the result into a different unit, such as \(\text{L/s}\).

Worked example

Problem. Water flows through a pipe with a cross-sectional area of \(0.20\,\text{m}^2\) and a velocity of \(3.5\,\text{m/s}\). Find the volumetric flow rate.

1. Start with \(Q = A v\).
2. Substitute the values, \(Q = 0.20 \times 3.5\).
3. Compute \(Q = 0.70\,\text{m}^3/\text{s}\).

Tips and common mistakes

• Make sure the area is the cross-sectional area perpendicular to the flow, not the surface area of the whole object.
• If your velocity is in \(\text{cm/s}\) or your area is in \(\text{cm}^2\), convert first so the final units are consistent.

Frequently asked questions