This calculator estimates flow from pressure with an orifice or nozzle model. Because pressure alone does not define flow, diameter, discharge coefficient, fluid density, and outlet count are included.
Calculator inputs
Example data table
| Pressure (PSI) | Diameter (in) | Cd | Specific Gravity | Nozzles | Estimated Flow (GPM) |
|---|---|---|---|---|---|
| 20 | 0.125 | 0.62 | 1.000 | 1 | 1.293 |
| 40 | 0.125 | 0.62 | 1.000 | 1 | 1.828 |
| 60 | 0.1875 | 0.62 | 1.000 | 1 | 5.038 |
| 80 | 0.250 | 0.62 | 1.000 | 1 | 10.342 |
| 100 | 0.3125 | 0.62 | 1.000 | 1 | 18.067 |
Formula used
This tool uses the common orifice or nozzle equation for incompressible flow. It estimates discharge based on pressure, nozzle size, coefficient of discharge, and fluid specific gravity.
Q = 29.84 × Cd × d² × √(P / SG)
Where:
- Q = flow in GPM per nozzle
- Cd = discharge coefficient
- d = nozzle or orifice diameter in inches
- P = pressure in PSI
- SG = specific gravity relative to water
For multiple nozzles:
Total Flow = Q × Number of Nozzles
Rearranged forms used by the reverse modes:
P = SG × (Q / (29.84 × Cd × d²))²
d = √(Q / (29.84 × Cd × √(P / SG)))
These formulas are suitable for quick engineering estimates. Real systems can differ because of piping losses, upstream restrictions, temperature, cavitation, and non-ideal outlet geometry.
How to use this calculator
- Select the calculation mode that fits your task.
- Choose a fluid preset or enter a custom specific gravity.
- Enter pressure, target flow, or diameter as needed.
- Set the discharge coefficient and number of nozzles.
- Press Calculate now to show results above the form.
- Review the table, curve, and converted values.
- Export the result table as CSV or PDF when needed.
Frequently asked questions
1. Can PSI be converted directly to GPM?
Not by itself. Flow depends on outlet geometry and fluid properties. This calculator adds nozzle diameter, discharge coefficient, specific gravity, and nozzle count so the estimate becomes physically meaningful.
2. What does discharge coefficient mean?
The discharge coefficient adjusts ideal flow to match real behavior. Sharp-edged openings often use values near 0.61 to 0.62, while smoother nozzles can be higher.
3. Why does specific gravity affect flow?
Heavier fluids resist acceleration more than water at the same pressure. When specific gravity rises, estimated flow drops because the square-root term uses pressure divided by specific gravity.
4. Can I use this for pumps and long pipes?
Use it as a quick outlet estimate. Pipe friction, valves, elevation change, and pump curves can materially change actual flow, so detailed hydraulic analysis may still be required.
5. What unit combinations are supported?
You can enter pressure in PSI, bar, kPa, or MPa. Flow supports GPM, LPM, and m³/h. Diameter supports inches, millimeters, and centimeters.
6. What does hydraulic horsepower show?
Hydraulic horsepower estimates ideal fluid power at the calculated flow and pressure. It helps compare operating intensity, though motor power needs are usually higher after efficiency losses.
7. Why does the graph curve upward slowly?
Flow changes with the square root of pressure in this model. Doubling pressure does not double flow, so the curve rises gradually rather than forming a straight line.
8. When should I choose custom specific gravity?
Choose custom when your liquid differs from the preset options or when you already know the exact specific gravity from test data, a specification sheet, or process documentation.