Reynolds Number Calculator
💨 Gas Laws & Fluids. Use the Reynolds number formula to find reynolds number, density ρ, speed, pipe diameter, viscosity μ: pick the value you want, type the others, and the answer updates as you go.
Below ~2000 the flow is smooth (laminar), above ~4000 turbulent.
Pick the ○ next to the value you want to find, fill in the others, and it solves as you type.
What each letter means
| Quantity | Unit |
|---|---|
| Reynolds number | no unit |
| Density ρ | kg/m³ |
| Speed | m/s |
| Pipe diameter | m |
| Viscosity μ | Pa·s |
Worked example
Find the reynolds number when Density ρ = 1000 kg/m³, Speed = 0.1 m/s, Pipe diameter = 0.02 m, Viscosity μ = 0.001 Pa·s.
Using Re = (ρ v D)/μ: Reynolds number = 2000.
Frequently asked questions
What is the formula for Reynolds number?
Re = (ρ v D)/μ. Below ~2000 the flow is smooth (laminar), above ~4000 turbulent.
What do the letters stand for, and what units are used?
Reynolds number, Density ρ in kg/m³, Speed in m/s, Pipe diameter in m, Viscosity μ in Pa·s.
How do you calculate reynolds number?
Put the values into Re = (ρ v D)/μ. For example, with Density ρ = 1000 kg/m³, Speed = 0.1 m/s, Pipe diameter = 0.02 m, Viscosity μ = 0.001 Pa·s, reynolds number = 2000.
Can I solve for a different value?
Yes. In the calculator above, pick the circle next to any value (reynolds number, density ρ, speed, pipe diameter, viscosity μ) and fill in the others: it rearranges the formula for you.
