Method and variables
Continuity equation: Q = A × v. For a circular pipe, A = πD² / 4.
- Q — volumetric flow rate
- A — internal cross-sectional area
- v — mean flow velocity
- D — actual internal diameter
Worked example
For 1.5 L/s through a 50 mm internal diameter, the area is 0.001963 m². The mean velocity is 0.0015 / 0.001963 = 0.764 m/s.
What this is for
Use it for early pipe and duct checks, comparing diameter options, and preparing inputs for a more complete pressure-loss calculation.
Important limits
The tool assumes a full circular flow path and reports mean velocity only. It does not account for pressure loss, pipe roughness, fittings, elevation, pump curves, two-phase flow, non-circular ducts or gas compressibility.
References
- OpenStax: Flow Rate and Its Relation to Velocity
- NIST Guide for the Use of the International System of Units
Related tools
Reynolds Number Calculator · Hydrostatic Pressure Calculator · Fluids & Piping Calculators
Frequently asked questions
How do you calculate flow velocity in a pipe?
Use v = Q / A, where Q is volumetric flow rate and A is the internal cross-sectional area. For a circular pipe, A = πD²/4.
Should I enter nominal or internal pipe diameter?
Enter the actual internal diameter. Nominal sizes and wall thicknesses differ by material, schedule and standard, so they cannot be substituted automatically.
Does this calculate pressure loss?
No. Continuity relates flow, area and velocity. Pressure loss additionally depends on fluid properties, length, roughness, fittings and flow regime.