Diffusion coefficient converter
Convert a diffusion coefficient between cm²/s and SI units, and see how far a molecule wanders in an hour.
That's 100× as fast as a protein in water, while salt in water is 1.5× faster. In an hour a molecule would wander about 2.683 mm.
What it means
How fast does it spread?
Diffusion distances go with the square root of time: four times as long gets you only twice as far.
Every unit
Your coefficient in every unit
Learn
Three things worth knowing
-
Distance = √(2Dt)
Doubling the distance takes four times the time. Diffusion is quick over micrometers and hopeless over meters.
-
Einstein, 1905
In the same year as relativity, he showed that the jittering of pollen grains under a microscope gave the size of atoms. Diffusion is that jitter, added up.
-
Cells are small for a reason
A protein crosses a bacterium in a second and a human body in decades. Every organism bigger than a millimeter needs a pump.
Shortcuts
Popular diffusion conversions
Background
About diffusion coefficients
A diffusion coefficient has the odd units of area per time, because diffusion distance grows with the square root of time: distance = √(2Dt).
Salt in water is about 1.5 × 10⁻⁵ cm²/s, which means a molecule wanders roughly 1 cm in a day. That is why stirring exists.