What is the Reynolds number for an airfoil?

The Reynolds number (Re) for an airfoil is Re = (V × c) / ν, where V is the freestream velocity, c is the chord length, and ν is the kinematic viscosity of the fluid. It is dimensionless and characterizes the ratio of inertial to viscous forces in the boundary layer.

What flow regimes correspond to different Re values for airfoils?

Below about 100,000 the flow is highly viscous and difficult to keep attached — typical of insects and micro-air vehicles. From 100,000 to 500,000 the flow is transitional; laminar separation bubbles are common. Above 500,000 to 1,000,000 the boundary layer transitions to turbulent on the forward portion of the chord. Above 1,000,000 the flow is largely turbulent from near the leading edge, as on most full-size aircraft.

What kinematic viscosity should I use for air?

At sea level and 15°C (59°F) standard atmosphere, air has a kinematic viscosity of about 1.461 × 10⁻⁵ m²/s (1.572 × 10⁻⁴ ft²/s). Kinematic viscosity increases with altitude (lower density) and decreases slightly with temperature. This calculator provides common presets for sea-level standard, hot day, and high altitude.

Why does Reynolds number matter for choosing an airfoil?

Airfoil performance depends strongly on Re. Profiles optimized for full-size aircraft (Re > 1,000,000) often perform poorly on model aircraft or UAVs (Re < 200,000) because the boundary layer behaves differently. Low-Re airfoils like the Eppler or Selig series are specifically shaped to manage laminar separation bubbles.

How is airfoil Re different from pipe flow Re?

The formula is the same (Re = V × L / ν), but the characteristic length L is the chord length for airfoils versus the hydraulic diameter for pipe flow. The critical values also differ: pipe flow transitions around Re = 2,300, while airfoil boundary layers transition at much higher values (typically 500,000–3,000,000) depending on surface roughness and pressure gradient.

Reynolds Number Airfoil Calculator

Enter airfoil chord length, flow velocity, and kinematic viscosity to compute the Reynolds number and identify the flow regime.

Airfoil Parameters

Chord Length

Distance from leading edge to trailing edge along the mean chord line.

Freestream Velocity

m/s

Airspeed or wind tunnel velocity relative to the airfoil.

Kinematic Viscosity (ν)

m²/s

Air Condition Presets

Quick Scenarios

Reynolds Number

Enter chord length, velocity, and kinematic viscosity to compute Re.

Flow Regime Reference for Airfoils

Re Range	Regime	Typical Application
< 50,000	Creeping / viscous	Insects, bio-inspired MAVs
50k – 200k	Low Re	Micro UAVs, indoor models
200k – 500k	Transitional	RC gliders, small UAVs
500k – 2M	Early turbulent	Light aircraft, soaring gliders
2M – 10M	Fully turbulent	General aviation, turboprops
> 10M	High Re turbulent	Commercial jets, military aircraft

Summary

The Reynolds number (Re) is a dimensionless quantity that predicts whether airflow over an airfoil is laminar, transitional, or turbulent. For a given chord length and freestream velocity, Re = (V × c) / ν, where V is velocity, c is chord length, and ν is kinematic viscosity. Low Re (below ~500,000) favors laminar flow with less skin-friction drag but higher separation risk; high Re (above ~1,000,000) produces turbulent flow, which is more resistant to separation. This calculator supports metric and imperial units and covers air at multiple temperatures.

How it works

Enter the airfoil chord length (the distance from leading edge to trailing edge).
Enter the freestream flow velocity (airspeed or wind tunnel speed).
Select or enter the kinematic viscosity of air at your operating conditions.
The calculator applies Re = (V × c) / ν, converting units as needed.
The result shows the Reynolds number and identifies the flow regime.
Use the preset buttons to load common flight and wind-tunnel conditions instantly.

Use cases

Determine whether flow over a model aircraft wing is laminar or turbulent.
Select the correct NACA airfoil profile for a given Reynolds number range.
Validate wind tunnel test conditions against full-scale flight equivalents.
Assess boundary-layer behavior during UAV or drone airfoil design.
Compare model scale versus full scale Re when designing test articles.
Estimate transition point location for glider and sailplane wing sections.
Size airfoils for high-altitude long-endurance (HALE) aircraft operating at low Re.
Check flow regime assumptions before running a CFD simulation.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu