If you have a hard time telling the difference between kilometers, meters, and centimeters, you are really going to struggle with nanometers. At one-billionth of a meter, the nanometer is used to measure really small things:

• A sheet of paper is about 100,000 nanometers thick
• A strand of human DNA  is 2.5 nanometers in diameter
• There are 25,400,000 nanometers in one inch
• A human hair is approximately 80,000- 100,000 nanometers wide
• A single gold atom is about a third of a nanometer in diameter
• On a comparative scale, if the diameter of a marble was one nanometer, then diameter of the Earth would be about one meter
• One nanometer is about as long as your fingernail grows in one second

While we’re on the subject, let’s talk about picometers. There are one trillion of these little guys in every meter. At this size, picometers are primarily used in measurements in particle and quantum physics. Your typical atom measures between 62 and 520 picometers in diameter.

The Laser Interferometer Space Antenna (LISA) probe planned for launch in 2034 to directly detect gravitational waves is designed to measure relative displacements with a resolution of 20 picometers over a distance of 5 million kilometers.

source