What is an Angstrom?

If you thought the nanometer was small, you haven’t met the angstrom, but that’s probably because it preceded the nanometer. Named after Swedish spectroscopist and physicist Anders Angstrom (1814-1874), the angstrom is a legacy unit of measurement that equals one ten-billionth of a meter, or 1/10,000,000,000 of 3.28 feet. Put another way, it would take 245-million angstroms to equal one inch, 10-million angstroms to equal one millimeter, or 10,000 angstroms to equal one micron. And by now you’ve guessed that with a nanometer being one-billionth of a meter, it takes 10 angstroms to equal one nanometer.

In 1868 Anders Angstrom was studying solar radiation and compiled a chart of electromagnetic energy that measured light waves in increments of one ten-millionth of a millimeter. It was this unit of measurement that became known as the angstrom. Though the angstrom has been replaced by the nanometer as the unit of choice, it was traditionally used to measure very small objects such as atoms and chemical bonds in addition to light waves and the visible light spectrum.

For humans, visible light includes those wavelengths that fall between rich violet and deep red. Violet light, for example, measures in the 4000-angstrom range, while dark red is nearer to 7000 angstroms. Wavelengths at 5500 angstroms (exactly between the two extremes) would be yellow light, center to the visible light spectrum. Today, however, the visible light spectrum is more often expressed as ranging from 400 – 700 nanometers (nm).

To offer a few real-world examples on the angstrom, a very thin human hair of just 50 microns would be 500,000 angstroms thick. A sheet of paper is about one million angstroms thick, and a credit card is a whopping 8-million angstroms thick.

While the angstrom served its purpose and is still used in some technical fields, as early as 1978 the International Committee for Weights and Measure called for the retirement of this unit of measurement by requesting scientists refrain from applying the angstrom to new applications or fields where it wasn’t already in use. The American National Standard for Metric Practice also discouraged its use and today the angstrom is considered obsolete.