What this calculator does
Reynolds number works out ratio of inertial to viscous forces in a flow, and whether it is laminar or turbulent. Enter your own figures above and the answer updates as you type: nothing is fixed in the code, so the result reflects exactly the numbers you supply.
The formula this calculator evaluates is printed under the tool and explained below, so you can check the working by hand or reuse it in a spreadsheet.
The formula
FormulaRe = ρvL/μ = vL/ν
The inputs explained
| Field | What to enter |
|---|---|
| Fluid density (water = 1000) (kg/m³) | A number, measured in kg/m³. Starts at 1000. |
| Flow speed (m/s) | A number, measured in m/s. Starts at 2. |
| Characteristic length (pipe diameter, etc.) (m) | A number, measured in m. Starts at 0.05. |
| Dynamic viscosity (water at 20 °C ≈ 0.001002) (Pa·s) | A number, measured in Pa·s. Starts at 0.001002. |
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the answer changes with fluid density (water = 1000)
Every other input is held at the calculator’s starting values while fluid density (water = 1000) varies. Select any row to load that scenario into the calculator.
How the answer changes with fluid density (water = 1000)
| Fluid density (water = 1000) (kg/m³) | Reynolds number | Flow regime | Kinematic viscosity (ν = μ/ρ) |
|---|---|---|---|
| 500 | 49,900 | Turbulent (pipe flow: laminar < 2300, turbulent > 4000) | 0.00000200 m²/s |
| 750 | 74,850 | Turbulent (pipe flow: laminar < 2300, turbulent > 4000) | 0.00000134 m²/s |
| 1,000 | 99,800 | Turbulent (pipe flow: laminar < 2300, turbulent > 4000) | 0.00000100 m²/s |
| 1,500 | 149,701 | Turbulent (pipe flow: laminar < 2300, turbulent > 4000) | 0.00000067 m²/s |
| 2,000 | 199,601 | Turbulent (pipe flow: laminar < 2300, turbulent > 4000) | 0.00000050 m²/s |
| 3,000 | 299,401 | Turbulent (pipe flow: laminar < 2300, turbulent > 4000) | 0.00000033 m²/s |