How do I convert nm to um (micrometers) ?

Question

without using an online calculator... I need to show work converting 21nm to ___ um

Answer 1

nanometers are 10^-9
micrometers are 10^-6
so that means you basically move the decimal over three spaces
1000 nm = 1 um
100 nm = 0.1 um
1 um = 1000 nm
23 um = 23000 nm

So,
21 nm = 0.021 um

Answer 2

Times 10^-3