A nanometer is an incredibly tiny unit of measurement: one billionth of a meter. To understand how small that is, imagine slicing a single meter into a billion equal pieces. Each piece would be one nanometer long.

Scientists use nanometers to measure things far too small to see with the naked eye or even regular microscopes. A human hair is about 80,000 nanometers wide. A single cell in your body measures thousands of nanometers across. Viruses range from 20 to 400 nanometers. Individual atoms, the building blocks of everything around you, measure less than one nanometer.

Scientists often abbreviate nanometer as nm when writing. When you hear about nanotechnology, that means technology built at the nanometer scale: engineers designing microscopic machines or materials just a few atoms thick.

Understanding nanometers helps scientists work with DNA, develop new medicines, build faster computer chips, and study how materials behave at their smallest levels. It's a measurement that opens up an invisible world where the rules of physics sometimes work differently than they do at human scale.