Calculator Inputs
Formula Used
Velocity Pressure: VP = 0.5 × ρ × V²
- VP = velocity pressure
- ρ = fluid density
- V = flow velocity
Volumetric Flow Rate: Q = A × V
Mass Flow Rate: ṁ = ρ × Q
Velocity Head: h = VP / (ρ × g)
How to Use This Calculator
- Enter the airflow velocity and choose its unit.
- Select a fluid preset or enter a custom density.
- Choose the pressure unit for the displayed result.
- Enter flow area if you also want flow rates.
- Press the calculate button to view results and graph.
Example Data Table
Dry air density = 1.225 kg/m³, area = 0.35 m²| Velocity (m/s) | Density (kg/m³) | Area (m²) | Velocity Pressure (Pa) | Flow Rate (m³/s) | Mass Flow (kg/s) |
|---|---|---|---|---|---|
| 5 | 1.225 | 0.35 | 15.313 | 1.75 | 2.144 |
| 10 | 1.225 | 0.35 | 61.25 | 3.5 | 4.288 |
| 15 | 1.225 | 0.35 | 137.813 | 5.25 | 6.431 |
| 20 | 1.225 | 0.35 | 245 | 7 | 8.575 |
| 25 | 1.225 | 0.35 | 382.813 | 8.75 | 10.719 |
Frequently Asked Questions
1. What is velocity pressure?
Velocity pressure is the pressure caused by fluid motion. It represents kinetic energy per unit volume and is widely used in airflow, duct, and fan calculations.
2. Why does the calculator need density?
Density directly affects velocity pressure. Higher density creates higher pressure at the same speed, which is why air, gases, and other fluids produce different results.
3. Can I use this for ducts and ventilation work?
Yes. It is suitable for duct sizing checks, fan performance reviews, airflow balancing, and quick engineering estimates during design or field troubleshooting.
4. What happens if I leave area blank?
The calculator will still compute velocity pressure. Flow rate and mass flow depend on area, so those values become zero when no area is provided.
5. Which pressure unit should I choose?
Choose the unit that matches your project documents or instruments. Pascals are common in SI work, while psi and inches of water are also used in practice.
6. Is velocity pressure the same as static pressure?
No. Velocity pressure comes from motion. Static pressure is the force applied equally in all directions. Total pressure combines static and velocity pressure.
7. Why does the graph curve upward?
Velocity pressure follows the square of velocity. When speed increases, pressure rises much faster, so the plotted line becomes steeper as velocity grows.
8. Can this calculator handle custom fluids?
Yes. Select the custom density option and enter the known density. The calculator then uses that value for pressure, flow, and velocity head outputs.