What does undecillion mean?
An undecillion is an immense cardinal number whose value depends on the numbering system in use. Under the short scale, which is standard in the United States and in most modern international contexts, it equals 10^51, or 1 followed by 51 zeros. Under the long scale, traditionally used in parts of Europe and in older British usage, it equals 10^60. The word is normally encountered in mathematics, scientific discussion, or rhetoric expressing the vastness of a quantity: for example, a capacity may be described as being a number of undecillion possible states. Because the quantity is so difficult to visualize, the word also carries a deliberately exaggerated or futuristic tone and can suggest the near-immeasurable scale of modern data, space, or theoretical systems. Its principal usage difficulty is numerical rather than grammatical: readers must first determine whether the surrounding context follows the short scale or the long scale.
nounA cardinal number equal to 10^51 in the short scale. In the long-scale naming system, it equals 10^60.
- In the short-scale system, the cardinal number 10^51, equal to 1,000 followed by 51 zeros.
- In the long-scale system, the cardinal number 10^60, equal to 1,000 followed by 60 zeros.
"The estimate was staggering: it placed the total number of possible configurations at one undecillion."
"The theoretical capacity of the system was measured in undecillion possible states."
"Even the smallest contribution would amount to millions of dollars, while the total forecast ran into the undecillions."
The plural is grammatical but uncommon, since undecillion is more often used attributively, in modified forms, or as part of an expression of scale.
"The participants debated whether the totals were merely millions or undecillions."
One undecillion has 51 zeros in the short scale—but in the long scale, the same word represents a number with 60 zeros.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does undecillion come from?
The word was formed in English from the combining element undec-, derived from Latin undecim, meaning “eleven,” and the suffix -illion. The -illion series belongs to the European naming tradition extending through million, billion, and trillion, and ultimately draws on Latin mille, meaning “thousand.” Its development reflects the historical spread of the long-scale system, while its modern meaning is also standardized under the short scale.
Related word forms
How undecillion is actually used
Undecillion is primarily formal, mathematical, or rhetorical. Its numerical value depends on the short- and long-scale conventions; modern US and international usage generally favors the short scale, while the long scale remains familiar in some European and older British contexts. Because the word denotes an immense quantity, it is also used figuratively for exaggerated abundance.
Easily confused with undecillion
In the short scale, a decillion is 10^33, whereas an undecillion is 10^51, making an undecillion enormously larger.