Tap Flow Rate Calculator
Enter a measured reference flow and pressure, then estimate outlet flow at another pressure. Add a volume to estimate water use or fill time.
A QUICK WALKTHROUGH
How to use this tool
- Choose compatible pressure and flow units for both reference and target values.
- Enter the reference flow Qr, reference pressure pr, and target pressure p.
- Optionally enter a container volume to estimate water used or filling time.
Square-root pressure model
For the same fixed outlet, Q = Qr × √(p ÷ pr). The pressure ratio is p ÷ pr. This assumes the reference and target pressures are expressed in the same compatible pressure unit, and both flows use the same flow unit.
Water amount and fill time
If a volume is entered in a unit compatible with the flow unit, water use is that volume and fill time = volume ÷ flow. For example, L and L/min produce minutes. Convert units before calculating; the tool does not infer conversions.
Model limits
This is an estimate for a fixed outlet under comparable conditions. It does not account for pipe diameter, hose length, fittings, elevation, viscosity, supply limitations, valve position, transient behavior, or changing outlet geometry. It does not provide pipe-sizing, equipment-selection, safety, or regulatory conclusions.
GOOD TO KNOW
Common questions
Do pressure units need to match?
Yes. Use the same pressure unit for p and pr, such as bar with bar or psi with psi. Absolute versus gauge pressure is a separate engineering choice; use a consistent basis appropriate to your measurements.
Can I use any flow unit?
Yes, as long as Qr and the optional volume use compatible units. For example, L/min with L gives minutes; gal/min with gal also gives minutes.
Does this size a pipe or confirm a code requirement?
No. It only applies the stated square-root relationship to a fixed outlet and cannot determine pipe size, compliance, or suitability.