Calculator
Formula Used
Area: A = πD² / 4
Pressure head: Hₚ = ΔP / ρg
Available head: H = Hₚ − Δz
Orifice flow: Q = nCdA√(2gH)
Pipe flow: Q = nA√(2gH / (Cv + K + fL / D))
Reynolds number: Re = ρvD / μ
The pipe option estimates f with laminar friction and the Swamee-Jain turbulent relation. It repeats the calculation until friction and velocity settle.
How to Use This Calculator
- Select pipe mode for long pipes, orifice mode for short openings.
- Enter the measured pressure drop and select its unit.
- Add the inside diameter, outlet count, and fluid properties.
- Enter pipe length, roughness, fitting losses, and elevation change.
- Press Calculate to view flow, velocity, head, and Reynolds number.
- Use the CSV or PDF button to save the calculated result.
Example Data Table
| Use case | Model | Pressure | Diameter | Length | Other inputs |
|---|---|---|---|---|---|
| Garden hose estimate | Pipe | 45 psi | 0.75 in | 30 m | K = 4, roughness = 0.0015 mm |
| Tank outlet | Orifice | 25 kPa | 25 mm | 0 m | Cd = 0.62, elevation = 0 m |
| Filter pressure drop | Pipe | 20 kPa | 40 mm | 10 m | K = 2.5, elevation = 1 m |
Water Flow Rate From Pressure Guide
Pressure can move water through a pipe, nozzle, or small opening. This calculator turns that pressure into an estimated flow rate. It also shows velocity, pressure head, Reynolds number, and common flow units. These values help compare pumps, hoses, tanks, filters, and simple hydraulic layouts.
What The Calculator Measures
The tool first converts pressure into head. Head is the energy available per unit weight of water. A higher head usually gives more speed. The final flow also depends on diameter. A larger diameter gives more area, so the same velocity moves more water. The calculator accepts several pressure and length units. It then reports cubic meters per second, liters per minute, cubic meters per hour, and gallons per minute.
Why Losses Matter
Real systems lose energy. Pipe wall friction slows the stream. Bends, valves, meters, strainers, and fittings add minor losses. Elevation also matters. If the outlet is higher, some pressure lifts the water. If the outlet is lower, gravity helps the flow. The pipe model uses these losses with an iterative friction estimate. This gives a more useful result than a simple pressure only estimate.
Pipe And Orifice Modes
Use pipe mode when water travels through a pipe length. Enter roughness, length, and loss coefficients. Use orifice mode for a tank outlet, nozzle, plate hole, or short opening. The discharge coefficient adjusts for contraction and turbulence. A value near one means an ideal opening. A lower value means more loss at the opening.
Reading The Results
Velocity helps check noise, erosion, and practical pipe sizing. Reynolds number shows whether flow is laminar, transitional, or turbulent. Turbulent flow is common in water pipes. Laminar flow happens at low velocity, small diameter, or high viscosity. The design margin adds extra capacity for planning. It is not a code requirement.
Practical Use
Measure pressure as close to the flowing section as possible. Use pressure drop across the device when checking filters or restrictions. Enter realistic fitting losses. Compare several diameters before choosing pipe. The calculator gives engineering estimates. Final designs should be checked with field data, manufacturer curves, and local standards.
Review outputs after each change. Check uncertain pressure or diameter during site testing and commissioning.
FAQs
Can pressure alone determine flow rate?
No. Pressure must be paired with diameter, fluid density, elevation, and losses. A narrow pipe can have low flow even with high pressure. A short wide opening can pass much more water.
Which pressure should I enter?
Enter the pressure drop available to create flow. For an outlet to air, this is usually gauge pressure at the inlet. For a device, use pressure difference across that device.
What is the difference between pipe and orifice mode?
Pipe mode includes length, roughness, fitting losses, and friction. Orifice mode is for a short hole, nozzle, or tank opening. It mainly uses area, pressure head, and discharge coefficient.
What discharge coefficient should I use?
A sharp-edged orifice often uses about 0.61 to 0.65. Smooth nozzles may be higher. Use manufacturer data when available because geometry strongly affects the coefficient.
What is minor loss coefficient K?
K represents fittings and local restrictions. Bends, valves, entrances, exits, meters, and strainers all add loss. Add their coefficients together for the minor loss input.
Why is Reynolds number included?
Reynolds number indicates flow pattern. Low values suggest laminar flow. High values suggest turbulent flow. The pipe friction estimate depends on this flow pattern.
Is this calculator exact?
It gives an engineering estimate. Real systems may differ because of pipe age, entrance shape, valve position, air, temperature, or inaccurate pressure readings.
Can I use other liquids?
Yes. Change density and viscosity to match the liquid. The result will improve when those values match the actual operating temperature and mixture.