Water Velocity Calculator
Find how fast water moves through a pipe from the flow rate and the pipe's inside diameter.
Change the values and press Calculate to work out your own figures.
Enter the flow rate and the inside diameter.
Show the working
- velocity = flow ÷ (π × (diameter ÷ 2)²)
How to use it
Enter the flow rate and the inside diameter.
Lengths can be decimals, fractions or tape entries such as 12' 6 1/2" (in feet or inches). Prices are optional.
Key facts
velocity = flow ÷ (π × (diameter ÷ 2)²); ≈ 0.4085 × gpm ÷ diameter² (in)
Limits
Water lines are usually kept under about 5–8 ft/s to limit noise, erosion and water hammer.
Questions
How fast does 15 gpm flow in a 3/4 in pipe?
10.89 ft/s.
Formulas
velocity = flow ÷ (π × (diameter ÷ 2)²); ≈ 0.4085 × gpm ÷ diameter² (in)
Sources
Limitations
- Material densities are typical values (the midpoint of the commonly published range); real loads vary with moisture, grading and compaction, so check with your supplier or type in their density.
- Tank results are the geometric volume; real tanks have wall thickness and fittings.