Calculator Inputs
Choose a target variable, enter known values, then submit.
Pressure and Velocity Trend Graph
The curve uses the selected density and current units.
Example Data Table
These examples use the incompressible flow assumption.
| Scenario | Pressure | Density | Diameter | Velocity | Flow Rate |
|---|---|---|---|---|---|
| Water transfer line | 25 kPa | 998 kg/m³ | 100 mm | 7.08 m/s | 0.0556 m³/s |
| Light oil pipeline | 18 kPa | 850 kg/m³ | 80 mm | 6.51 m/s | 0.0327 m³/s |
| Glycol circulation loop | 12 kPa | 1035 kg/m³ | 65 mm | 4.82 m/s | 0.0160 m³/s |
Formula Used
Primary relation: ΔP = 0.5 × ρ × v²
This links pressure differential, fluid density, and velocity pressure for incompressible flow.
Solve velocity: v = √(2 × ΔP ÷ ρ)
Solve pressure: ΔP = 0.5 × ρ × v²
Solve density: ρ = 2 × ΔP ÷ v²
Pipe area: A = π × D² ÷ 4
Volumetric flow: Q = A × v
Mass flow: ṁ = ρ × Q
Reynolds number: Re = ρ × v × D ÷ μ
Use these formulas for incompressible fluids, moderate losses, and negligible elevation effects. Compressible gases need a more advanced model.
How to Use This Calculator
- Select whether you want to solve velocity, pressure differential, or density.
- Enter the known values and choose matching measurement units.
- Add pipe diameter to estimate area, flow rate, and mass flow.
- Enter viscosity to estimate Reynolds number and flow regime.
- Press calculate to show the result section above the form.
- Download the result summary with the CSV or PDF buttons.
Frequently Asked Questions
1. What does this calculator solve?
It solves one missing variable in the velocity pressure relation. It also estimates pipe area, volumetric flow, mass flow, Reynolds number, and a basic flow regime label.
2. Which pressure value should I enter?
Enter the pressure differential tied to velocity pressure, not total system pressure. The model uses the change in pressure that converts into fluid motion.
3. Can I use this for gases?
Use caution with gases. This page assumes incompressible behavior. For high gas speeds, wide pressure changes, or compressibility effects, use a dedicated compressible flow method.
4. Why is diameter included?
Diameter is not required for the core pressure and velocity equation. It is included to derive pipe area, volumetric flow rate, mass flow rate, and Reynolds number.
5. What is Reynolds number used for?
Reynolds number helps classify the likely flow regime. Lower values suggest laminar flow, middle values suggest transition, and higher values suggest turbulent behavior.
6. Why do my results look unrealistic?
Check units first. A common issue is mixing kPa, bar, and psi, or mm and m. Also confirm that density and viscosity match the fluid temperature.
7. Does the graph update with my inputs?
Yes. The graph uses your selected pressure and velocity units, plus the active density. It also marks the current operating point when values are available.
8. What do the export buttons save?
The export buttons save the visible result summary table. CSV is useful for spreadsheets, while PDF is useful for reports, emails, or meeting notes.