how small is a nanometer

A nanometer is extremely small—specifically, it is one billionth of a meter (0.000000001 meters or 10−910^{-9}10−9 meters). To put it in perspective, a human hair is about 60,000 to 100,000 nanometers wide, a DNA molecule is about 2.5 nanometers in diameter, and a water molecule is less than one nanometer across. Thus, nanometers are used to measure objects at the atomic and molecular scale, such as atoms, molecules, and viruses, which cannot be seen with the naked eye or even with standard microscopes.