Calculates the Stokes-Einstein diffusion coefficient D = kT/(6πηr) for a spherical particle of radius r in a solvent of viscosity η. A 1 nm radius protein in water at 25 °C has D ≈ 2.1 × 10⁻¹⁰ m²/s — larger particles diffuse more slowly; at 10 nm, D drops 10-fold.
Inputs
Temperature C
Thermal state of the substance. Check whether the formula needs Celsius, Fahrenheit, or Kelvin (K = °C + 273.15).
Viscosity Cp
Fluid resistance to flow. Water at 20°C: ~1 cP. Honey: 2,000–10,000 cP. Higher viscosity increases pumping power requirements.
Particle Radius Nm
Distance from centre to edge of a circle. Radius = diameter / 2.
Results
diffusion coefficient D (m²/s)
Sample size or count used in the calculation.
diffusion coefficient (µm²/s)
Sample size or count used in the calculation.
D = kBT / (6πηr)
Reference formula or conversion factor shown for context.
mean displacement in 1s (µm)
Arithmetic average — sum divided by count. Simple and familiar, but pulled by outliers. If your data contains extreme values, the median may be more representative.