ONE FORMULA, ONE ANSWER
Reynolds Number Calculator
Check flow similarity in pipe experiments and scale models. Choose input units and calculate one value within the stated conditions.
Inputs
Calculations run in this browser. Scientific notation such as 1.2e-3 is supported. Do not group thousands.
Result
Reynolds number Re
Enter values and select Calculate.
Re = ρ V L / μ
Assumptions
Use ρ,L,μ>0 and V≥0. For internal circular-pipe flow, use the inside diameter for L. Pipe-flow transition thresholds do not apply unchanged to flat plates or external flows. This tool returns Re only; it does not certify laminar flow.
Displayed values are floating-point approximations. Measurement uncertainty and design safety factors are not calculated.
Formula references and credits
NaNa Lab created the code, descriptions, icons and preview images. Text, figures and code from the linked references have not been reproduced.
Physical constants: NIST / CODATA 2022. The values of μ₀ and ε₀ are measured recommendations, not exact defining constants. Values and precision notes are in the source record.
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