nanogram

A nanogram (ng) is a unit of mass equal to one billionth of a gram, or 10^-9 g. In SI terms, the prefix nano- denotes 10^-9, and the nanogram is a derived unit based on the gram. Since the kilogram is the SI base unit for mass, a nanogram is equivalent to 10^-12 kilograms. The symbol for the unit is ng.

Nanograms are used to express very small masses in science and medicine. They appear in chemistry, biology, pharmacology, environmental science, and materials science for quantities that are too small to be conveniently measured in micrograms or milligrams. Common applications include measuring trace substances, quantifying nanomaterials, and estimating the mass of extracted DNA, proteins, toxins, or drug substances at low concentrations. In molecular biology, DNA quantities are frequently reported in nanograms.

Measurement and conversion considerations are important. Weighing a mass at the nanogram level requires highly sensitive instruments or indirect analytical methods; direct gravimetric weighing is typically impractical without specialized equipment. In common conversions, 1 ng equals 10^-12 kg, and 1000 ng equals 1 μg (microgram). For perspective, a single human cell contains about 6 picograms of DNA, so 1 nanogram corresponds to roughly several hundred cells’ worth of DNA (depending on ploidy).

The nanogram remains a practical unit for reporting small masses in laboratory contexts, bridging the gap between microgram measurements and even smaller, nanoscale quantities.