Flow Rate Calculator
A tap, hose or pump’s flow in gallons or litres a minute from a bucket test, or from the water’s speed in a pipe, and how long it takes to fill something.
Result
10 gpm
A bucket test measures the flow at that tap and pressure only.
https://calcgallery.com/home-systems/flow-rate-calculator/
Results are estimates for planning only. Actual needs vary with site conditions, products and workmanship. Always confirm quantities with your supplier and follow local building codes and manufacturer instructions. Read the full disclaimer
How to use the Flow Rate Calculator
- For a bucket test, open the tap or hose fully, time how long it takes to fill a bucket of known size, and enter the volume and the time.
- For a pipe, enter its inside diameter and the water's speed, or switch mode to find the speed from a flow you know.
- Enter a volume to fill, such as a pool or tank, to see how long it will take.
The formulas
bucket test flow = volume collected ÷ timepipe flow = speed × π × (inside diameter ÷ 2)²speed speed = flow ÷ (π × (inside diameter ÷ 2)²)fill time time = volume to fill ÷ flowEverything is converted to cubic metres and seconds first, so a gallon bucket timed in seconds gives litres a minute or gallons an hour just as readily. One US gallon a minute is exactly 3.785411784 litres a minute.
What the page does not do
It does not work out pressure, friction loss or the pipe size a job needs. Those depend on the pipe material, its length, the fittings and the elevation, and are the business of the fixture maker’s data and a plumbing designer.
With your numbers
- Flow = volume collected ÷ time taken
Quick reference
A bucket test measures the flow at that tap and pressure only.
| Job | Result |
|---|---|
| 5 gal bucket in 30 seconds | Flow rate: 10 gpm |
| 5 gal bucket in 1 minute | Flow rate: 5 gpm |
| 1 gal in 10 seconds | Flow rate: 6 gpm |
| 1 in pipe at 5 ft/s | Flow rate: 12.24 gpm |
| Speed of 10 gpm in a 1 in pipe | Water speed in the pipe: 4.08 ft/s |
| 20,000 gal pool at 10 gpm | Flow rate: 10 gpm |
| 10 L in 12 seconds | Flow rate: 50 L/min |
| 25 mm pipe at 1.5 m/s | Flow rate: 44.18 L/min |
Common questions about the Flow Rate Calculator
- How do I measure the flow rate of a tap or hose?
- Time how long it takes to fill a container of known size. A 5-gallon bucket that fills in 30 seconds is 5 ÷ 0.5 = 10 gallons a minute. Use the biggest container you have and time it more than once: a small jug fills too fast to time accurately.
- How long will it take to fill my pool with a hose?
- Divide the pool’s volume by the hose’s flow. A 20,000-gallon pool at 10 gallons a minute takes 2,000 minutes, over 33 hours. Enter the pool volume under volume to fill; the pool volume page works it out from the pool’s size.
- How is flow related to the speed of water in a pipe?
- Flow is speed times the pipe’s inside area. Water at 5 feet a second in a pipe with a 1-inch bore is 12.24 gallons a minute. The same flow in a pipe with half the bore moves four times as fast, because the area is a quarter.
- Why is my measured flow lower than the pump's rating?
- A pump’s rated flow is at a stated head or pressure. Height, pipe length, fittings and filters all add resistance, and the flow falls as they do. A bucket test at the outlet measures what actually arrives.