Fluid flow is a key component in measuring the performance of a plumbing system. Everything from a pump in a jetted bathtub to a large water main is rated based on how much water it can move in a given period of time. High-pressure systems deliver more water, but also require more substantial construction to better withstand the pressure that the water places on them. To compare systems and capabilities, look at their CFM (cubic feet per minute) rating, which you may need to derive for systems that report in pounds per seconds.

Measure the flow rate as accurately as possible with a tool that gives you a result in pounds per second. Alternatively, you can use a pre-specified measurement if you have one available.

Multiply the pounds per second measurement by 60, which is the number of seconds in a minute. The result of this calculation is the flow rate measured in pounds per minute.

Divide the pounds per minute measurement by 62.4. This will give you the measurement in cubic feet per minute, or CFM.