Here's the breakdown:

* Nano means one billionth (1/1,000,000,000).

* Milli means one thousandth (1/1,000).

Therefore, there are 1,000,000,000 nanometers in 1 millimeter. To find how many millimeters are in one nanometer, you divide 1 by 1,000,000,000, which gives you 1/1,000,000 or 0.000001 millimeters.