Free online tool to calculate pipe flow velocity v = Q / (A × PF), the flow rate for a target velocity, or the pipe diameter you need. Supports round and rectangular ducts, sensor profile factors, DN presets and ideal-gas conversion of operating to standard flow.
Cross-sectional area of round pipe or rectangular duct
A = π × d² / 4Area A = 0.007854 m² (78.54 cm²)Standard flow or operating condition data
Flow velocity distribution coefficient across pipe cross-section
Profile factors account for the non-uniform velocity profile in turbulent pipe flow:
When converting operating flow (Q_op) to standard conditions (20 °C, 1013.25 hPa):
Allows seamless normalization between compressed line conditions and standard reference m³/h.
Recommended industrial velocity standards for industrial fluids:
The tool solves the same equation three ways. Pick the mode that matches what you know, fill in the inputs, and the result updates as you type. Every result comes with the formula substitution so you can check it or paste it into a sizing report.
Know the flow rate and the pipe? Enter both to get the line velocity in m/s, ft/s and km/h, rated against the recommended range for air, gas, steam or water. Use this to check an existing line or to confirm a thermal-mass or insertion sensor will see enough velocity.
Know the pipe and the velocity a sensor reads? Get the volumetric flow in m³/h, m³/s and L/s. Handy for converting a velocity reading from a probe into a flow figure.
Know the flow you must carry and the velocity you want to stay at? Get the required inner diameter, plus the next standard DN size up and the velocity you'd actually get in it.
Tip: for compressed air measured at line pressure, switch to Operating Data (Gas Law) and enter the gauge pressure and temperature; the calculator converts to standard flow (Nm³/h) before computing velocity.
Divide the volumetric flow rate by the pipe's cross-sectional area: v = Q / A. For a round pipe A = π × d² / 4. Convert Q to m³/s (divide m³/h by 3600) and d to metres so the result is in m/s. Thermal and insertion sensors also apply a profile factor (PF), giving v = Q / (A × PF).
Explore IOTAFLOW’s range of Electromagnetic, Vortex, Ultrasonic, and Thermal Mass flow meters engineered for high accuracy and 7-day fast delivery.