quettagram
An SI unit of mass equal to 10³⁰ grams. Symbol: Qg
Quettagram: the SI unit for incomprehensibly large masses
A quettagram is a unit of mass in the International System of Units (SI) equal to 1030 grams, or one nonillion grams in short scale. Its symbol is Qg. The term entered official SI vocabulary in 2022 when the General Conference on Weights and Measures added four new extreme-range prefixes to handle both astronomical and subatomic scales in a uniform way. The quetta prefix, like its counterpart ronna (1027), was adopted to extend SI coverage upward; quetta comes from the Latin word for ten.
In practical terms, a quettagram exists almost nowhere in ordinary work. One quettagram approximates the mass of Jupiter, or roughly 318 times the mass of Earth. To put this in context, the entire global human population weighs about 400 megatons, or 4 × 108 kg; Jupiter weighs about 1.9 × 1027 kg, which is 1.9 × 1021 times heavier. The quettagram is a theoretical unit created for astronomical and cosmological calculations, not for laboratory or industrial measurement.
Why it exists and where it matters
Before 2022, SI had a symmetry problem. On the small end, prefixes extended down to yocto (10-24), covering subatomic and quantum scales relevant to physics research. On the large end, the highest prefix was yotta (1024), which stopped short of the masses commonly cited in astrophysics. Adding quetta (1030) and ronna (1027) closed that gap and extended SI's reach to objects and phenomena studied in cosmology and stellar science. A quettagram or quettameter now allows physicists and astronomers to express cosmic scales without resorting to scientific notation or ad-hoc units.
Metrology and standards bodies view the quettagram as part of long-term system coherence. Its adoption reflects the principle that SI should be complete and future-proof, even for domains, such as astrophysics, that rarely need it in daily practice. The unit is rarely encountered in industrial inspection, laboratory calibration, or commercial trade; it serves instead as a reference point for consistency across scientific disciplines and as a hedge against the need for new prefixes decades hence.