How to calculate the flow rate of your pump – Allflo Pumps & Equipment

Whether you’re assessing an existing industrial pump system or planning a new installation, flow rate is one of the most important performance parameters to understand.

Flow rate determines how much fluid a pump can move over time and directly affects system efficiency, reliability, and correct pump selection.

This guide explains how to calculate the flow rate of your pump, why it matters, and how to measure it accurately in real-world industrial applications. 

Why should I calculate the flow rate?

Flow rate is the volume of fluid a pump can move within a given time. Understanding this value helps you:

• Assess system performance
  Compare expected flow rate with actual flow rate to identify underperformance or inefficiencies.

• Confirm correct system design
  Ensure the pump and pipework are correctly sized to deliver the required volume under operating conditions.

How to calculate the required flow rate before installation

Before selecting a pump or engaging a manufacturer, defining the required flow rate is essential for correct system design.

Incorrect flow rate calculations can result in:

• Oversized pumps with unnecessary energy consumption

• Undersized pumps that fail to meet demand

• Increased wear, maintenance, and operating costs

Before ordering a pump, three factors must be considered together:

• Fluid characteristics – Is the fluid clean or viscous? What temperature will it operate at?
• System layout – Pipe length, elevation changes, and friction losses.
• Required volume over time – How much fluid must be moved within a specific period.

Together, these factors determine the required flow rate and directly influence pump size, configuration, and efficiency.

If you’re unsure how these variables apply to your application, Allflo offers free pump sizing guidance to help ensure the right pump is selected from the outset.

How to calculate the flow rate of an existing pump system?

If a system needs to move 300 litres in 30 minutes:

Example:
If a system needs to move 300 litres in 30 minutes
→ 300 ÷ 30 = 10 litres per minute
→ 0.167 litres per second

This is the desired flow rate.

Once the pump is installed, monitor the flow rate periodically to determine if your pump is performing efficiently. 

You can measure the flow rate of an operating pump using one of the following methods:

• Flow meter
  Installed on the discharge line, a flow meter measures the volume of fluid passing through the system.

• Manual collection method
  Collect fluid at the discharge point, measure the volume collected and the time taken, then calculate:

Flow rate (L/min) = Volume collected (L) ÷ Time taken (min)

If there is a significant difference between the required flow rate and actual system performance, this may indicate wear, blockage, incorrect sizing or operating issues.

If measured flow rates don’t align with system requirements, it often points to incorrect sizing, system losses, or wear — all of which can be assessed before failure occurs.