Calculate flow rate from differential pressure across orifice plates, Venturi tubes, flow nozzles, and Pitot tubes. Converts ΔP to flow velocity and volume.
Differential pressure (DP) flow measurement exploits Bernoulli's principle: when fluid accelerates through a constriction, its static pressure drops in proportion to the square of its velocity. By measuring the pressure difference across the constriction and knowing the geometry, you can calculate the flow rate precisely.
This calculator supports four primary DP flow devices. The orifice plate is the simplest and most common — a thin plate with a concentric hole. Venturi tubes recover most of the pressure, reducing energy loss. Flow nozzles offer a middle ground, and Pitot tubes measure point velocity directly from velocity pressure ½ρV². Each device has a characteristic discharge coefficient (Cd) that accounts for real-flow effects.
Input your differential pressure in Pa, kPa, psi, inH₂O, or mmHg, and the calculator returns flow velocity, volume flow rate (L/s, L/min, gpm, m³/h), and the discharge coefficient used. The ΔP-vs-flow chart illustrates the square-root relationship between pressure and flow.
Differential-pressure flow measurement is used in over 30% of industrial flowmeters worldwide. This calculator helps engineers size orifice plates, check Venturi meters, and convert DP readings to flow rates.
This tool is designed for quick, accurate results without manual computation. Whether you are a student working through coursework, a professional verifying a result, or an educator preparing examples, accurate answers are always just a few keystrokes away.
Orifice / Venturi / Nozzle: Q = Cd × E × A_d × √(2ΔP / ρ) E = 1 / √(1 − β⁴), β = d/D Pitot tube: V = √(2ΔP / ρ) Where: • Cd = discharge coefficient • A_d = orifice area (m²) • ΔP = differential pressure (Pa) • ρ = fluid density (kg/m³)
Result: Q ≈ 0.76 L/s, V ≈ 0.97 m/s
A_d = π/4 × (0.05)² = 1.963×10⁻³ m². E = 1/√(1−0.0625) = 1.033. Q = 0.61 × 1.033 × 0.001963 × √(10000/998) ≈ 0.00393 m³/s ≈ 3.93 L/s — actual numbers vary with precise Cd iterations.
Use consistent units throughout your calculation and verify all assumptions before treating the output as final. For professional or academic work, document your input values and any conversion standards used so results can be reproduced. Apply this calculator as part of a broader workflow, especially when the result feeds into a larger model or report.
Most mistakes come from mixed units, rounding too early, or misread labels. Recheck each final value before use. Pay close attention to sign conventions — positive and negative inputs often produce very different results. When working with multiple related calculations, keep intermediate values available so you can trace discrepancies back to their source.
Enter the most precise values available. Use the worked example or presets to confirm the calculator behaves as expected before entering your real data. If a result seems unexpected, compare it against a manual estimate or a known reference case to catch input errors early.
Beta (β) is the ratio of the orifice bore diameter d to the pipe diameter D. It typically ranges from 0.2 to 0.75. Higher beta means less pressure loss but also less measurement signal.
Bernoulli's equation gives ΔP ∝ V² for incompressible flow. Inverting: V ∝ √ΔP. This means doubling the flow quadruples the differential pressure. Understanding this concept helps you apply the calculator correctly and interpret the results with confidence.
For a sharp-edged orifice, Cd ≈ 0.61. Machined Venturi tubes achieve Cd ≈ 0.985. Exact values depend on Re and β — standards like ISO 5167 provide detailed correlations.
A Pitot tube faces into the flow and measures the stagnation pressure minus static pressure (velocity pressure). It gives point velocity, not average velocity, and causes minimal flow disturbance.
The Venturi's gradual convergence and divergence minimize boundary-layer separation and turbulence, letting the actual flow rate very nearly match the theoretical prediction. Understanding this concept helps you apply the calculator correctly and interpret the results with confidence.
Yes, but for compressible gases at high pressure ratios (ΔP/P > ~10%), apply an expansion factor (ε or Y) to correct for gas density change through the restriction. Use this as a practical reminder before finalizing the result.