How this calculator works
Classical equipartition assigns kBT/2 to each translational degree of freedom. Three-dimensional translation therefore has mean kinetic energy 3kBT/2, giving the RMS speed through one-half m times the mean squared speed. This is a statistical speed, not the drift of the whole gas. Use the mass of one particle, or divide molar mass by the Avogadro constant.
Formula
vrms = sqrt(3kBT/m); T = m vrms²/(3kB); m = 3kBT/vrms².
Worked example
A hypothetical particle of mass 4.141947e-23 kg at 1 K has RMS speed 1 m/s. At 4 K, the same particle has RMS speed 2 m/s.
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Frequently asked questions
Is this every particle speed?
No. The gas has a distribution of speeds; RMS is the square root of their mean square.
Can I enter atomic mass units?
Convert them to kilograms using approximately 1.66053906892e-27 kg per unified atomic mass unit.
Does it apply to light or relativistic particles?
No. It assumes classical nonrelativistic translational motion.