Plumbing Flow Rate
Estimate the flow rate of a pipe from pressure and diameter.
About Plumbing Flow Rate
Pressure first becomes an equivalent water head in feet, which drives the flow velocity. That velocity times the pipe cross-section area yields gallons per minute. Estimating flow helps size drain systems, plan irrigation and judge whether a fixture will keep up with demand.
Formula
Plumbing Flow Rate
Velocity = sqrt(2 x g x head); flow = velocity x pipe area
- head
- Pressure converted to feet of water column
Worked example
With the default values below, Plumbing Flow Rate returns Pressure Head of 115.5. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Water pressureminimum 0 psi
- 50 psi
- Pipe inner diameterminimum 0.01 inches
- 0.5 inches
Results
- Pressure Head
- 115.5 ft
- Flow Rate
- 52.8 gpm
- Water Velocity
- 86.2 ft/s
- Flow Rate (GPH)
- 3,166.7 gal/hr
Step by step
- 1Values used
- 2Plumbing Flow Rate
- 3Pressure Head= 115.5 ft
- 4Flow Rate= 52.8 gpm
- 5Water Velocity= 86.2 ft/s
- 6Flow Rate (GPH)= 3,166.7 gal/hr
Assumptions and limits
- The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 1 decimal place, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Plumbing Flow Rate calculated?
Velocity = sqrt(2 x g x head); flow = velocity x pipe area Pressure first becomes an equivalent water head in feet, which drives the flow velocity. That velocity times the pipe cross-section area yields gallons per minute.
Why does Plumbing Flow Rate matter?
Estimating flow helps size drain systems, plan irrigation and judge whether a fixture will keep up with demand.
What values do I need to enter?
This calculator takes 2 inputs: Water pressure, Pipe inner diameter. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.