Flow Rate Calculator (GPM)
Calculate Gallons Per Minute quickly and accurately.
How to Calculate Flow Rate in Gallons Per Minute
Flow rate is a measurement used to determine how much liquid passes through a specific point within a set amount of time. In the United States, the most common unit for plumbing, well pumps, and irrigation systems is Gallons Per Minute (GPM).
The GPM Formula
The "Bucket Test" Method
If you are trying to find the flow rate of a faucet, showerhead, or outdoor hose, the easiest way is the bucket test:
- Get a container with a known volume (like a 5-gallon bucket).
- Use a stopwatch to time how long it takes to fill the bucket to the top.
- Convert the seconds into minutes (divide seconds by 60).
- Divide the container size (gallons) by the total minutes.
Real-World Example
Suppose you fill a 5-gallon bucket from your garden hose, and it takes 45 seconds.
- Step 1: Convert 45 seconds to minutes. 45 / 60 = 0.75 minutes.
- Step 2: Divide gallons by minutes. 5 / 0.75 = 6.67 GPM.
Why GPM Matters
Knowing your GPM is essential for sizing water softeners, selecting the right pool pump, or ensuring your irrigation system has enough pressure to pop up sprinkler heads. Low GPM can indicate pipe clogs or pump failure, while excessively high GPM can lead to water waste and high utility bills.