Pipe velocity
This result uses the pipe's internal cross-section. It is an average, not the centerline velocity or a local velocity near fittings.
Engineering Tool · Pipe Flow
Pipe Flow Velocity & Reynolds Number Calculator
Calculate mean velocity from actual volume flow and pipe inside diameter, or find flow from velocity. Add fluid viscosity to estimate Reynolds number, with flow unit conversions in the same calculation.
Use the inside diameter and actual operating flow. This tool is for a full, circular pipe with steady, single-phase Newtonian flow. Gas flow and fluid properties must refer to the same operating temperature and pressure.
Enter pipe conditions
One set of inputs for velocity, flow conversion and Reynolds number.
Pipe flow results
Mean cross-section velocity and a circular-pipe flow reference.
Flow cross-section—πD²/4
Mean velocity—Through the full pipe bore
Actual volume flow—At operating conditions
Reynolds number—Dimensionless
Flow regime reference
—
These conventional pipe thresholds are guides. Inlet disturbances, geometry and operating conditions affect transition.
Equivalent actual flow rates
—
Formulas and basis
A = πD²/4 · v = Q/A · Q = vA
Re = vD/ν = ρvD/μ · ν = μ/ρ
Internal units: D in m, Q in m³/s, v in m/s, ν in m²/s, μ in Pa·s and ρ in kg/m³.
Use the right flow area
Filter face velocity
Flow through a filter uses its active filtration area. Use the filter area and face velocity calculator for that calculation.
Actual gas flow
Nm³/h, Sm³/h and scfm require a stated reference condition. Convert them with the standard-to-actual gas flow calculator before using this tool.
Worked example
For an inside diameter of 50 mm, actual flow of 10 m³/h and kinematic viscosity of 1 cSt: A = 0.0019634954 m², mean velocity = 1.4147106 m/s and Re = 70,735.53. This is a turbulent pipe-flow reference. The same viscosity can be entered as μ = 1 cP and ρ = 1,000 kg/m³.
These are illustrative inputs. Enter fluid properties at your actual temperature and pressure; the calculator does not infer properties from a fluid name.
Frequently asked questions
Should I use nominal pipe size, outside diameter or inside diameter?
Use the actual inside diameter. Nominal pipe size is a designation and does not equal the bore diameter. Wall thickness, pipe schedule, liners and deposits can change the internal area.
What does the Reynolds number mean here?
It compares inertial and viscous effects using mean pipe velocity and inside diameter. This tool labels Re below 2,300 as a laminar reference, 2,300 through 4,000 as transition and above 4,000 as a turbulent reference for circular pipe flow.
Can I calculate velocity without knowing viscosity?
Yes. Disable “Include Reynolds number” and enter actual flow and inside diameter. The continuity calculation v = Q/A requires no density or viscosity.
Are cP and cSt interchangeable?
No. cP measures dynamic viscosity and cSt measures kinematic viscosity. Convert using density: ν = μ/ρ in consistent SI units. Equal numerical cP and cSt values occur only at density 1,000 kg/m³.
Can I use this for sintered filters or perforated support tubes?
The bore calculation can describe axial flow through a pipe-like tube, but not flow through its perforations or porous wall. Circular-pipe Reynolds thresholds must not be applied directly to porous media. Use perforated tube effective open area to estimate clear hole area; filter pressure drop requires additional media data and validation.
Does the calculator predict pressure drop or select a safe pipe diameter?
No. It computes geometry, continuity and Reynolds number. Pressure loss and pipe selection additionally require length, roughness, fittings, fluid properties, compressibility where relevant and service-specific design criteria. Review flow rate and pressure drop estimates for that tool's stated basis.
Can I use the flow conversions for gas?
Yes, if all values describe actual volume at the same temperature and pressure. Conversion changes units, not gas reference conditions. US and Imperial gallons are separate units.
Formula references
NASA Glenn: Reynolds number and viscosity relationship · Caleffi: circular-pipe Reynolds reference ranges · NIST: unit conversion factors.
Metal components for filtration systems
Explore perforated tubes and metal filter elements. For manufacturing review, share the drawing, material, dimensions and operating conditions.
Discuss your specificationsEngineering estimate for full, circular pipes with steady, single-phase Newtonian flow. Excludes open-channel, partially filled, non-Newtonian, two-phase and strongly compressible flow, and porous-media flow. Results do not establish filter efficiency, allowable velocity or guaranteed pressure drop.
