How small is the smallest microchip? How large are vaccine needles?

[Chronos]

And while we’re at it, \Omega and \omicron, “Omega” and “omicron”, are literally “Big O” and “Little O”.

@Francis_Vaughan

There is no unit, metric or imperial that makes sense with a micro prefix.

Not true: A microchip could very easily be a square one micromile on a side.