What does duodecillion mean?
Duodecillion is a cardinal number naming an astronomically large quantity: 10^39, or a 1 followed by thirty-nine zeros, under the short-scale system used in the United States and modern Britain. In the older long-scale system once current in Britain, the same word denoted the far larger value of 10^66. The word is built from Latin elements — 'duodecim', meaning twelve, plus the '-illion' ending borrowed from million — marking it as the twelfth number in the -illion sequence after decillion. In practice, duodecillion rarely describes anything countable; it functions mostly in mathematics, astronomy, and popular science to convey scale beyond intuition, and informally as hyperbole for 'countless' or 'an immense amount'. Like its siblings trillion and septillion, it is useful precisely because ordinary words for 'very many' fail at such magnitudes, though writers should note the scale ambiguity when exactness matters.
The number equivalent to 10^39 in the short scale (or 10^66 in the historical long scale).
"A mole of moles would weigh on the order of a duodecillion kilograms."
In precise scientific writing, state the exponent explicitly, as the long-scale and short-scale values differ.
Amounting to one duodecillion in number or quantity.
"The simulation tracked duodecillion possible outcomes."
Pluralizes normally when referring to multiple instances of the number or indefinite huge quantities.
"The dataset contains duodecillions of data points, far more than any analyst could review."
A duodecillion is so large that even counting one number per second since the Big Bang would barely get you started — and in old British usage it meant a thousand times bigger still.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of duodecillion
Duodecillion derives from the Latin 'duodecim', meaning 'twelve', combined with '-illion', the ending abstracted from 'million' (itself from Old French, ultimately from Latin 'mille', 'thousand'). The pattern was extended systematically in early modern English to name successive powers of a thousand, with 'duodecillion' coined as the twelfth such term. Its cousins across the series — decillion, undecillion, tredecillion — share the same Latin numeral roots, as do unrelated-looking words like 'duodecimal' and 'dozen'.
Related word forms
How duodecillion is actually used
Duodecillion belongs almost entirely to formal mathematical and popular-science writing, where large-number names follow the -illion series; outside those registers it appears mainly as playful hyperbole. Because its value differs between the short scale (10^39) and the older long scale (10^66), careful writers specify which convention they mean when precision matters.
Easily confused with duodecillion
A decillion is 10^33 in the short scale, whereas a duodecillion is far larger at 10^39; the 'duodeci-' prefix marks it as the twelfth member of the -illion series.