// multi-utility computation suite · offline · instant · precise
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sci.collision-cross-section Calculator
Calculates the collision cross-section of molecules from their diameters and estimates mean free path in a gas. Mean free path λ = kT / (√2 π d² P) — at atmospheric pressure and 25 °C, nitrogen molecules travel ~66 nm between collisions.
Inputs
Diameter1
Distance across a circle through its centre. Always confirm units match the rest of the calculation.
Diameter2
Distance across a circle through its centre. Always confirm units match the rest of the calculation.
Pressure
Force per unit area (Pa). Atmospheric pressure at sea level: 101,325 Pa. Check whether gauge or absolute pressure is required.
Temp
Thermal state of the substance. Check whether the formula needs Celsius, Fahrenheit, or Kelvin (K = °C + 273.15).
Results
collision cross-section (m^2)
Sample size or count used in the calculation.
mean free path (nm)
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.
number density (m^-3)
Sample size or count used in the calculation.
sigma = pi*((d1+d2)/2)^2
Reference formula or conversion factor shown for context.