zeptogram

A zeptogram (symbol zg) is a unit of mass in the SI system, corresponding to 10^-21 grams, which is equivalent to 10^-24 kilograms. It is derived from the SI prefix zepto-, meaning 10^-21. The prefix is part of the extended set of decimal multipliers used for naming very small masses.

Zeptograms are rarely used in everyday measurements; in practice, scientists typically employ attograms (10^-18 g) or even smaller units such as yoctograms (10^-24 g) for ultra‑precise mass discussions. Because zeptograms are so small, measurements at this scale require highly specialized instrumentation and are more common in theoretical calculations or in converting between units in highly precise nanoscale contexts.

Conversions and scale: 1 zeptogram equals 1×10^-21 g, which is also 1×10^-24 kg. It is equal to 0.001 attograms and 1000 yoctograms. In terms of magnitude, one zeptogram is roughly the mass of about six hundred protons, illustrating how minuscule this unit is in practical terms.

Notes on usage: The zepto prefix and the zeptogram are part of the formal SI naming conventions but are not commonly encountered outside specialized fields such as high-precision mass metrology or theoretical discussions of subatomic scales. They illustrate the completeness of the SI system for expressing extremely small masses alongside more familiar units like grams and kilograms.