Input Parameters
Results
| # | Differential Pressure | Fluid Density | Flow Element | Flow Coefficient | Diameter | Velocity (m/s) | Velocity (ft/s) | Velocity (km/h) | Velocity (mph) | Flow (m³/s) | Flow (L/s) | Flow (CFM) |
|---|
Example Data
This table shows typical velocities for air at different differential pressures using density 1.204 kg/m³ and flow coefficient equal to one.
| Differential Pressure (Pa) | Fluid Density (kg/m³) | Flow Coefficient | Velocity (m/s) |
|---|---|---|---|
| 25 | 1.204 | 1.0 | 6.42 |
| 50 | 1.204 | 1.0 | 9.08 |
| 100 | 1.204 | 1.0 | 12.84 |
| 200 | 1.204 | 1.0 | 18.15 |
Formula Used
This calculator is based on Bernoulli's principle for incompressible flow, relating velocity to differential pressure across a measuring device such as a Pitot tube, orifice plate, or Venturi tube.
The ideal relationship is:
v = √(2 · ΔP / (ρ · C²))
where v is velocity (m/s), ΔP is differential pressure (Pa), ρ is fluid density (kg/m³), and C is the flow coefficient accounting for device and installation effects.
For volumetric flow, the cross-sectional area A is computed from the internal diameter, and:
Q = v · A
where Q is volumetric flow rate (m³/s). Additional unit conversions are then applied to obtain liters per second and cubic feet per minute.
How to Use This Calculator
- Measure the differential pressure across your flow element using a suitable transmitter or gauge.
- Enter the measured value in the differential pressure field and select the correct unit from the list.
- Choose a fluid preset to auto-fill density, or keep the custom option and enter your own density and unit.
- Select the flow element type so that a suitable coefficient suggestion can be applied.
- Adjust the flow coefficient if you have specific calibration or manufacturer data.
- Optionally enter the pipe or duct internal diameter and its unit to compute volumetric flow rate.
- Choose which velocity units you want to display, from a single unit to all four at once.
- Press the Calculate Velocity button to compute the flow speed and, if available, volumetric flow rate.
- Use the CSV or PDF buttons to export your calculation history for reporting, documentation, or further analysis.
- Use the Reset button to clear the form and start a new series of calculations.
Introduction to Differential Pressure Flow Measurement
Differential pressure devices infer flow by measuring pressure drop between two points. This calculator converts those readings into velocity, helping you understand how fast air, water, or other process fluids move through pipes, ducts, and channels in real engineering installations. It replaces repetitive hand calculations and reduces mistakes in fast-paced everyday design work.
Relationship Between Pressure Difference and Fluid Velocity
According to Bernoulli’s principle, higher differential pressure corresponds to higher fluid speed. The calculator applies the square root relationship between pressure and velocity, correcting for density and flow coefficient, so you can translate sensor readings into meaningful, engineering-ready velocity values.
Importance of Accurate Fluid Density Selection
Density strongly influences computed velocity because the same pressure drop accelerates light and dense fluids differently. By allowing custom density and helpful presets, the tool supports laboratory conditions, design calculations, or operating scenarios where temperature, composition, or pressure modify fluid properties significantly.
Choosing and Interpreting Flow Coefficients
Real flow elements introduce losses, surface roughness, and geometric effects. The coefficient parameter captures these influences. Preset suggestions for Pitot tubes, orifice plates, Venturi tubes, and averaging probes give quick starting values while still permitting fine-tuning to match field calibration or manufacturer documentation.
From Velocity to Volumetric Flow Rate
When internal diameter is known, the calculator multiplies velocity by cross-sectional area to estimate volumetric flow. Results in cubic meters per second, liters per second, and cubic feet per minute simplify communication between design engineers, commissioning teams, and operations personnel reviewing airflow or liquid transport capacity.
Practical Uses in HVAC, Process, and Energy Systems
Typical applications include balancing air distribution in ducts, sizing fans, validating chilled water circuits, monitoring fuel or gas feeds, and troubleshooting performance in industrial equipment. Storing results as CSV or PDF helps document test points, trend behavior over time, and support compliance or maintenance reporting.
Good Practices When Interpreting Calculator Results
Always confirm sensor calibration, tap locations, and straight-run requirements for the chosen element. For compressible gases at very high velocities or large pressure drops, consult detailed standards or specialist software. Treat calculator outputs as guidance, then combine them with engineering judgment and site experience. Compare several readings at different loads to check system behavior trends.
Frequently Asked Questions
What does this differential pressure to velocity calculator do?
This calculator converts differential pressure measurements into fluid velocity, and when diameter is entered, into volumetric flow. It helps quickly interpret readings from Pitot tubes, orifice plates, Venturi meters, and similar elements in HVAC, industrial, laboratory, and energy applications.
When should I change the fluid density value?
Change the density whenever temperature, pressure, or composition differ from standard reference conditions. Using realistic density values ensures that the velocity and flow results match actual process behavior instead of idealized textbook assumptions, especially for gases or warm liquids.
How accurate are the default flow coefficient suggestions?
Suggested coefficients are typical values taken from common design practice. Real installations may differ because of wear, tap locations, or fabrication tolerances. Whenever possible, adjust the coefficient using manufacturer data, commissioning tests, or site calibration reports for the specific flow element installed.
Can I use this tool for gases at high pressure?
Yes, but caution is required for highly compressible flows. For large pressure drops or velocities approaching sonic conditions, simple incompressible formulas may not be sufficient. In those cases, consult detailed standards, manufacturer software, or a specialist engineer before relying on the results.
Why is volumetric flow not displayed in my results?
Volumetric flow appears only when a valid internal diameter is entered. Without that diameter the calculator computes velocity at the measurement location but cannot estimate flow rate. Double-check that the diameter value and its unit are set correctly, then run the calculation again.
How should I export and store calculation results?
Use the CSV export when you want to analyze multiple points in spreadsheet software. Choose the PDF export when you need a fixed, shareable report for documentation, commissioning records, or regulatory files that captures the exact numbers used during testing.