EngineerHub.orgWhat this calculator does
The calculator uses continuity, Q = AV, for a circular pipe. Pipe presets can populate the actual bore from a common size series, while liquid and gas presets populate density and viscosity for mass flow and Reynolds number. All values remain visible and editable.
Inputs
Select a representative size family or enter the actual inside diameter directly.
Choose a representative liquid/gas or override the properties with project data.
Results
Velocity limits are application-specific. Noise, erosion, water hammer, solids, allowable pressure drop and pump economics may control the design.
Background
Engineering basis, property presets, interpretation and limitations.
For a circular pipe, A = πD²/4 and V = Q/A. The velocity head is V²/(2g). Pipe material does not appear in these equations; it matters here only because different dimensional standards give different inside diameters for the same nominal size.
The dimensional presets are convenience values for early screening. Carbon/stainless steel use a representative ASME-style NPS Schedule 40 bore table; copper uses representative Type L tube dimensions; HDPE uses an IPS SDR 11 relationship. PVC/CPVC use representative Schedule 40-style bores. Ductile iron and custom selections default to direct-ID entry because actual bore depends strongly on pressure class, lining and product standard.
For final work, use the actual inside diameter from the governing pipe/tube standard, piping class, manufacturer data, lining thickness and corrosion allowance.
Density and viscosity presets are representative values at the reference condition shown beside the selector. They are intended to make the calculator convenient for screening, not to replace a property package.
Gas warning: gas density changes strongly with absolute pressure, temperature and composition. A gas preset at 1 atm should not be used directly for compressed-gas service. Enter density and viscosity at the actual operating condition.
Re = ρVD/μ. This tool labels flow as laminar below 2300, transitional from 2300 to 4000, and turbulent above 4000. These thresholds are standard screening conventions for internal flow in a round pipe; disturbances and developing flow can shift transition behavior.
There is no universal acceptable velocity. Appropriate limits depend on service: noise, erosion, solids transport, corrosion, cavitation margin, water hammer, pressure drop, pump/compressor energy and equipment-nozzle limits can all control the design.
- Use velocity as an early sizing indicator, not a stand-alone acceptance criterion.
- Check pressure drop with Darcy–Weisbach or an applicable service-specific method.
- For gases, consider compressibility and Mach number when pressure drop or velocity becomes significant.
Frequently Asked Questions
Practical questions about pipe presets, fluid properties and interpretation.
Velocity is Q/A, so it depends on volumetric flow and the actual inside diameter. Material matters indirectly because the selected pipe standard and wall series determine the bore.
No. Treat it as a screening convenience. Verify the actual inside diameter from the applicable pipe or tube standard, piping class and manufacturer data.
Not directly. The listed gas properties are reference-condition values near 20 °C and 1 atmosphere. Enter density and viscosity at the actual operating pressure, temperature and composition.
The preset is only a starting point. Project-specific temperature, concentration, pressure or composition can materially change fluid properties, so the fields remain editable.
No. It calculates the hydraulic quantities. Acceptable velocity must be selected from project criteria considering pressure drop, noise, erosion, transients, solids, corrosion and equipment limits.