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One of the answers in a reading exercise in my class today was:

  • 100,000,000,000,000,000,000

... which was the value of the highest denomination note ever issued. It was a 100,000,000,000,000,000,000 Pengo note, issued by Hungary in 1946. The students in my class wanted to know how they could say that last sentence in words in English. So I told them that I didn't know. They pointed out to me that if they wanted to read this bit of writing to someone they'd want to be able to use the words. Fair point.

Can anyone help?

[In case you're interested, a 100,000,000,000,000,000,000 Pengo note was worth about $0.20!]

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It's:

one hundred quintillion

or:

a hundred quintillion

The words for very large numbers

If you're wondering how to form other huge numbers like this, here's the pattern:

A thousand thousands is a million: 1,000,000.

A thousand millions is a billion: 1,000,000,000.

A thousand billions is a trillion: 1,000,000,000,000.

A thousand trillions is a quadrillion: 1,000,000,000,000,000.

A thousand quadrillions is a quintillion: 1,000,000,000,000,000,000.

A thousand quintillions is a sextillion: 1,000,000,000,000,000,000,000.

And so on. The part before -illion is the Latin prefix for the number of times you went through the process of multiplying by a thousand. So, you can continue to septillion, octillion, nonillion, decillion, undecillion, duodecillion, and so on forever.

Within the scale defined by one of these huge units, you multiply by a number from 1 to 999 in the usual manner, by putting the multiplier ahead of the unit, and you add smaller numbers by putting them after the unit, in the same manner as for thousands:

215,002 is "two hundred fifteen thousand and two".

215,000,000,000,000,000,002 is "two hundred fifteen quintillion and two".

The usual customs for "hundred" apply:

123,456,100,000,000,000,000 is "a hundred and twenty-three quintillion four hundred and fifty-six quadrillion one hundred trillion" or "one hundred twenty-three quintillion four hundred fifty-six quadrillion one hundred trillion", or other variations, the same as for hundreds of thousands.

Exponents

When you work with these numbers on a daily basis like I do,* you soon find that they become rather unwieldy, at least until you get up to a centillion pengős.† In the physical sciences, if not in economics, one normally writes and pronounces these numbers using powers of ten. A quintillion is 1018, which you pronounce like this:

Ten to the eighteenth power.

Ten to the eighteenth. [for short]

Ten to the eighteen. [even shorter]

In scientific notation, you always choose an exponent large enough so the multiplier has one digit to the left of the decimal point, like this: 2.15 ⨉ 1017. That's pronounced:

215 quadrillion is "two point one five times ten to the seventeenth."

If the multiplier is exactly 1, you can omit it in speech. So:

100,000,000,000,000,000,000 is a hundred quintillion, or ten to the twentieth power.

Does anybody really say “quintillion”?

“Quintillion” is an obscure word, though not much more obscure than “quadrillion”, which often gets totted out when government budgets and monetary inflation make news. A fluent speaker can guess it from the pattern of “billion”, “trillion”, etc. Here are a few samples to illustrate typical contexts where people really use it to communicate (that is, not just to talk about words for huge numbers, which might be its most frequent use):

Government budgets: “For instance, the expected state income for oil and gas was reduced from 99,591 quintillion rupiah (about 9 billion euro) to 72,930 quintillion rupiah.”

Pop science: “The quantum simulation of the 69 electrons must specify all possible 600 quintillion states simultaneously.”

Bizarre religious tracts: “When this universe collapses in 70–100 billion years from now Jesus has given Kush a Quintillion universes like the one we live in as its territory forever. That is our promised land.”

Very low probabilities resulting from calculations: “Using FBI statistics, Schoon calculated that the DNA profile at issue would be found in 1 in 2.7 quintillion African-Americans, 1 in 52 quintillion Caucasians and 1 in 260 quintillion Hispanic unrelated individuals.” (This is from a U.S. appellate court opinion.)

Often when “quintillion” appears in print, it’s accompanied with an explanation. Usually when I’ve seen it used without explanation, it’s been in the context of economics. Presumably that crowd is well accustomed to talking about vast sums of money.

Long scale and short scale

Notice that in the Indonesian budget described above, “quintillion” occurs with multipliers greater than 999. That suggests that they're following the “long scale” system, in which each successive ‑illion is a million times greater than the previous one. That's an older usage, now nonstandard in English in all countries, but some people still use it, especially in countries like Indonesia where the dominant language follows the long-scale system. See kasperd's answer for more about that.

*Just kidding.

†When you get up to a centillion pengős, you're talkin’ real money.

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  • 3
    but some system uses millions as the word counting basis: eg 1 million (10^6) is a million, a million million (ie 2 of them or 10^12) is a billion, a million million million (3 of them or 10^18) is a trillion, etc. I'm not sure which is more common but IIRC British use my definition of billion, and Americans use yours (ie a thousand times multiplier for each word step)
    – gbjbaanb
    Jun 24, 2015 at 13:31
  • The classical usage is for naming structures to contain 1 order of magnitude greater quantity than the prevous, hence 999 thousand is in thopusands and 1000 thousand is a million, using the classical naming rules, it is 100 trillion. The rules above are in effect the american financial scales. Shall post a better answer later on:)
    – GMasucci
    Jun 24, 2015 at 14:15
  • FWIW, my English instructor always stated the word and should only separate wholes and decimals: "One Thousand Two Hundred Fifteen and twelve-one-hundredths" or some such. Is that regional, and I've been wrong this whole time, or grammatically correct, yet uncommon?
    – phyrfox
    Jun 24, 2015 at 16:11
  • @phyrfox "And" can precede whatever comes after "hundred". For example, "a hundred and twenty-five". Here is a question about it. Instructors often make things seem more rule-like than they really are, because of the difficulties of running an orderly class.
    – Ben Kovitz
    Jun 24, 2015 at 18:17
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    @Gloria The custom in chemistry is to use Greek prefixes: mono-, di-, tri-, tetra-, penta- and so on (except for 9 and 11 (!) and except for 1–4 for carbon chains). A few of these prefixes are the same or similar in both sequences, though: tri-/tri-, octo-/octo-, dec-/deca-, undec-/hendeca-, duodec-/dodeca- etc. Solid shapes in geometry also follow Greek: tetrahedon, dodecahedron, etc. This page has lots more information about the sequences and when each is customarily used in English.
    – Ben Kovitz
    Jun 26, 2015 at 14:42
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Wikipedia lists large scale numbers here.

As only the 10x with x being a multiple of 3 get their own names, you read 100,000,000,000,000,000,000 as 100 * 1018, so this is

  • 100 quintillion in American and British English and
  • 100 trillion in most (non-English speaking) other places.

(Practical approach: The different naming patterns for large numbers obviously can lead to misunderstandings internationally, expressing large numbers in the unambiguous format of X×10y may be preferrable in these cases. )

Some additional information on the Hungarian money for your students: Wikipedia (in the same article as above) claims that the highest note issued was actually 10 times as "valuable":

The highest numerical value banknote ever printed was a note for 1 sextillion pengő (1021 or 1 milliard bilpengő as printed) printed in Hungary in 1946.

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    In what parts of the world is long scale numbering still in use among English-speakers?
    – choster
    Jun 23, 2015 at 14:30
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    @choster Problem is that these terms are very similar or even identical in many languages. If I (German) read "billion" I think "1,000,000,000,000" whereas my (US) counterpart means "1,000,000,000". It's always a good idea to keep this in mind, these misunderstandings are surprisingly common. Being wrong by a factor of 1,000 (or even more for trillion etc.) is no picknick.
    – Stephie
    Jun 23, 2015 at 14:48
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    And as Britain switched from long to short scale in the 1970s, it's good to double-check for older documents which scale was used...
    – Stephie
    Jun 23, 2015 at 15:12
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    "One hundred million million millions" would be safe. And lots of people wouldn't know what 100 quintillion is.
    – gnasher729
    Jun 23, 2015 at 16:00
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    @gnasher729 "Quintillion" is obscure word, but not so unheard-of that it doesn't occasionally make it into New York Times headlines. Please see comments here for why "million million millions" is at least as unsafe, and my answer for some more detail about the obscurity of "quintillion".
    – Ben Kovitz
    Jun 23, 2015 at 19:00
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You can call it a hundred million million million.

The three million in a row can be a bit confusing, which is why the word trillion was invented. Trillion is a contraction of tri (meaning three) and million. That would make the name a hundred trillion.

Unfortunately some languages including English have redefined the word trillion to mean 1 000 000 000 000. And simultaneously redefined the word quintillion to mean 1 000 000 000 000 000 000.

This means there are now two different names for that number, and each name has a totally different meaning to somebody else. Which means you can use either word and people will know that you are talking about a big number, but nobody will be quite sure which number you are talking about.

You could also call it a tenth of a trilliard which to the best of my knowledge is unambiguous.

If it is important that the person you are speaking to know exactly which big number you have in mind, it is best to use mathematical terms in which case the name will be ten to the twentieth (power).

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    Indeed it is a tragedy that "billion" came to mean "a thousand millions", since the bis- prefix is Latin for "twice" and "billion" was a nice way of saying "a million, twice". (I understand the contracted prefix in "trillion" to be ter-, which is Latin for "thrice", but that's just me.) Do you know how the Americans came to use -illion for thousand (sort of)? I've never read anything on how it happened.
    – Ben Kovitz
    Jun 23, 2015 at 19:38
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    @BenKovitz Wikipedia mentions trimillion and tryllion as older spellings if trillion. I don't know how the Americans came up with a different meaning. I am guessing it started as a mistake and there may have been nobody around to notice and correct the mistake at first.
    – kasperd
    Jun 23, 2015 at 22:12
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    I found this in the OED: "According to Littré, it was only in the middle of the 17th c. that the ‘erroneous’ custom was established of dividing series of figures above a million into groups of three, and calling a thousand millions a billion, and a million millions a trillion, an entire perversion of the nomenclature of Chuquet and De la Roche." Littré seems to be the author of a French dictionary.
    – Ben Kovitz
    Jun 24, 2015 at 1:38
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    Found something: Florian Cajori says it grew out of the 17th-century French custom of dividing numbers into periods of three digits instead of six. The French apparently "perverted" the excellent terminology they invented, and the U.S. copied.
    – Ben Kovitz
    Jun 24, 2015 at 1:43
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    @BenKovitz Littré wrote a dictionary that still defines the standards of writing good literature in French (though it was updated a bit since). Now the dictionary itself goes by the name of Littré, like "I checked that up in the Littré". Back to the issue, in France and most of Europe, the long scale is in use nowadays, even though, like you said, the short scale was used for a while back in the 17/18th centuries. It happens to be the time at which most of the settlers crossed to America, so I wouldn't be surprised it just stayed when Europe went back to long scale.
    – spectras
    Jun 27, 2015 at 15:38
12 
one hundred  quintillion

You can try all sorts of numbers on a site like this: http://saythenumber.com/?n=k2Y

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  • 2
    This doesn't answer the question. Stack Exchange sites aim to be a repository of information, not a link farm.
    – David Richerby
    Jun 23, 2015 at 18:47
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    I know disagreement will be useless from my part, but this directly answers the question.
    – engspeaker
    Jun 23, 2015 at 19:03
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    The answer to this question is a wiki link: Names of large numbers.
    – Mazura
    Jun 25, 2015 at 2:11
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    @Mazura: Links are never answers. Period.
    – Lightness Races in Orbit
    Jun 27, 2015 at 19:55
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Outside of mathematics, it is also common to read such a number as "one hundred million million million".

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    Common where? I have very seldom heard or read this sort of stacking, beyond the occasional poetic use, e.g. "a thousand thousand warriors".
    – Nathan Tuggy
    Jun 23, 2015 at 15:25
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    @NathanTuggy You should get out more, then! ;-)
    – Araucaria - Not here any more.
    Jun 23, 2015 at 16:10
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    I've tried using the "million million …" approach with native AmE speakers, and the result has always been instant confusion. The problem is that beyond a couple "million"s, the listener's short-term memory easily loses track. But if you want an amusing tidbit to add to this answer, a usage of "billion billion" occurs near the beginning of Monty Python's "Science Fiction Sketch".
    – Ben Kovitz
    Jun 23, 2015 at 18:03
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    Saying "million" three times in a row can be a bit confusing which is why another word was constructed for this. Taking tri (which means three) and million contracted to trillion simply substitutes for saying million three times in a row. Unfortunately somebody decided to redefine the word trillion to mean billion. Which leaves us mostly with ambiguous ways to express that number.
    – kasperd
    Jun 23, 2015 at 18:13
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    @NathanTuggy It's common in the British media. "... objects containing a million million atoms or more" (BBC); "1,000,000,000, 000,000,000,000,000,000. A thousand million million million million!" (The Guardian); "contributing approximately £12 million million to GDP" (Financial Times).
    – David Richerby
    Jun 23, 2015 at 19:36
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As others before me have said, there are names for very large numbers, but these are quite esoteric and people may not know what you're talking about. These names aren't like "thousand" or "million", unless you've sat down with a list and learned them, you probably won't know them. They just don't come up in day-to-day use. In my experience, they tend to be like English terms of venery. Some people have learned that you can say "a parliament of owls" to refer to a group of owls, but it's very rare to see these words in normal conversation. Usually they come up in quizzes and as a matter of trivia or curiosity.

I would be more likely to just read it, like englishimprover.com, as "a hundred million million million" - or "a hundred billion billion". Using google ngram, we can compare how commonly these terms are used.

It seems that quintillion is gaining in popularity, but million million million still outnumbers it

Billion billion vastly outnumbers quintillion

A word like duodecillion is a rare thing indeed. My spell checker doesn't know it

Of course, in a scientific, or economic, context, you could convert this into what's called "standard form". For simplicity and readability, most people working with large numbers stop using their names after a point - and, indeed, stop writing them out in digits. As Ben Kovitz says, you could simply read this as "one times ten to the twenty" (that's how we'd do it here in Britain), or "one hundred times ten to the eighteen" (less likely). We could also re-write it: 1 x 1020.

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  • I watch a lot of YouTube science content, and multiples of millions and billions is by far the most common way to read large numbers, like this example from Kurtzgesagt
    – gotube ♦
    Jul 18, 2022 at 17:18
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100,000,000,000,000,000,000 is 100×1018 or 100×103+(3×5), so this is "one/a hundred quintillion" to most English speakers around the world today (including those in the United States, United Kingdom, Canada, Australia, New Zealand, India, Pakistan, and Nigeria).

While many native English speakers will not know the rarely seen word, at least in the U.S. it is generally used when appropriate in mass media (e.g. newspaper articles), though often followed by a clarifying aside like "that's 100 million million millions" when the order is above "trillion". If you're teaching students, it's the perfect sort of word to introduce for the sake of expanding vocabulary, though I strongly recommend you connect it to the Latin prefixes to help it stick.

Due to the difference between the long and short scales, beware "false friend" words in other languages—especially French, in which the cognates are spelled identically—and when reading historical English text (written as recently as the 1970's in the case of the UK). For example, the French "100 trillion" translates to the English "100 quintillion", not the English "100 trillion".

Due to the possible confusion caused by the two scales, when clarity is particularly important and/or the audience particularly diverse, it's a good idea to also give the number in the unambiguous scientific notation (100×1018).

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I haven't seen anyone suggest it, yet, but I would just say this as "One times ten to the twentieth [power]," where [power] is optional. To me, this seems less confusing when dealing with numbers of magnitudes above the trillions. It doesn't run into any of the regional interpretation problems listed in the answers above regarding the meaning of 'billion' and so forth and it doesn't sound (to me) as awkward as saying "hundred million million million."

Incidentally, numbers are also commonly actually written that way. For example, scientists and engineers frequently write large numbers as 1.0 x 10^20 (or sometimes 1.0e20) rather than 100,000,000,000,000,000,000. No need to count the zeroes that way. This is commonly referred to as Scientific Notation.

As a side note, you know your currency has inflation problems when scientific notation is useful for listing normal amounts of money. :) I can just imagine seeing scientific notation on paper money or on a store receipt or cash register.

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    I guess you'd call that 'one-with-twenty-zeros', which is the most likely phrase to be understood.
    – Govert
    Jun 25, 2015 at 18:39
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one hundred quintillion

a hundred quintillion

This is the list of numbers (truncated):

  • ...
  • 1,000,000: a million
  • 1,000,000,000: a billion
  • 1,000,000,000,000: a trillion
  • 1,000,000,000,000,000: a quadrillion
  • 1,000,000,000,000,000,000: a quintillion
  • ...

In the above list, you can replace "a" with a number from zero to nine. That means to multiply a number with another, e.g.

  • two hundred = a hundred * two = 100 * 2 = 200
  • five billion = a billion * five = 1000000 * 5 = 5000000

"a" is the same as "one".

Using the information above, here is the compilation of 100,000,000,000,000,000:

  1. We see that the number has between 16 and 18 digits, so we're talking about A quintillion B.
  2. We then see that the digits to the right are all zeroes, so we omit B, staying with A quintillion.
  3. To find x, we look at the digits before the first digit separator. They are three digits, so we set A to C hundred D.
    1. The first digit of them is 1, so we set C to either one or a, having a hundred D.
    2. The other two digits are zeroes, omitting D (staying with a hundred).
  4. Our final result is a hundred quintillion.
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Different languages don't agree on the names of numbers 1,000,000,000 and larger. Therefore it's a good custom to express such large numbers using no bigger names than "million", since everyone in the world agrees on that. Otherwise non-native speakers might get confused, and not even all English speakers agree on the names of large numbers.

Following that principle, 100,000,000,000,000,000,000 would be pronounced as "one hundred million million million". This would avoid any possible international confusion, even if it is a little long.

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    It's especially bad when some text is translated from English say to German. If you read in German "eine Billion" you have absolutely no idea whether this is a correct translation of "one trillion" or an incorrect translation of "one billion", or a correct translation of "one billion" in an English text before 1960. And then you have no idea whether the original English writer knew what he was writing.
    – gnasher729
    Jun 11, 2016 at 19:08
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You could also say 100 Exa Pengo or 100 EP, like some people (particularly in economics) say $100K to say 100 000 dollars. It's not very common, but the advantage is that there's no ambiguity compared to trillion/quintillion.

This is not a usage you will often hear informally, but it can pop up in newspapers and economics papers.

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    No you couldn't. Just as you wouldn't say "ten kilodollars", "five megaeuro" or "nine gigapounds", you wouldn't say "one hundred exapengo".
    – David Richerby
    Jun 23, 2015 at 18:47
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    @DavidRicherby Well, technically, you could. Indeed in the U.S., I occasionally hear "kilobucks" and "megabucks". These are playful usages, of course, not meant to be precise. But one always has the option of inventing a new usage to suit the occasion. It just wouldn't be standard (at that time), and people might laugh at you. ;)
    – Ben Kovitz
    Jun 23, 2015 at 19:12
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    @kasperd I've heard "k" used ("He earns fifty k a year") but, in British English, I've never heard "kilo" on its own to mean anything other than a kilogram.
    – David Richerby
    Jun 23, 2015 at 19:29
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    It's a bit hard to search for $...K but here is a concrete example in the news for $100k: $100k search on Google News - 646K results for me (pun intended). So yes, as I said, it's not very common, but it's used in newspapers and economics academic papers, so I thought it should be proposed as a complementary answer here.
    – gaborous
    Jun 23, 2015 at 23:31
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    Megadollar, MUSD and GUSD are used. SI prefix + ISO 4217 code is unambiguous.
    – Cees Timmerman
    Jun 24, 2015 at 14:48
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As pointed out in several other answers and the comments on this answer, the words for very large numbers (billion, trillion, ...) have two different meanings depending on which variant of English you are speaking: long scale and short scale. Also, the words past "trillion" are rarely used and people may not remember what they mean. (Quick! How much is a vigintillion?)

Therefore, I strongly recommend use of scientific notation to say numbers larger than 100 million (100,000,000) out loud, because it's unambiguous and it's easier for people to think about. Count the number of digits in the number, then say "a times ten to the Nth", where a is the first digit of the number, and N is the number of digits minus one. If a is 1 you can just say "ten to the Nth". For instance, the face value of that Hungarian note was ten to the twentieth pengo.

If you need to, you can give more leading digits of the number by saying "a point b c" where a, b, and c are the first, second and third digits. Technically you can keep going with that as long as necessary, but I can't think of any situation where I would say more than three leading digits out loud. I might write 6.02214129 × 1023 on a chalkboard during a chemistry lesson, but I would still say "six point oh two times ten to the twenty-third."

Especially when speaking of money, people often use an even shorter form: "N figures" means "a number which is at least 10N but less than 10N+1." For instance, "he makes six figures a year" means he makes at least $100,000 a year but not more than $999,999 a year.

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    Hmm... I'd say, at least in the U.S., most people will understand 'trillion' just fine, but I agree that saying "ten to the x" is better for numbers larger than the trillions. Trillions are used commonly when describing the size of the economy, the federal budget, the size of hard drives, or, for Obama's first few years, even the federal budget deficit.
    – reirab
    Jun 24, 2015 at 15:52
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    @reirab See kasperd's answer -- in casual conversation, confusion between a short-scale billion (10<sup>9</sup>) and a long-scale billion (10<sup>12</sup>) probably isn't going to be a huge deal, but when you hit trillions (10<sup>12</sup> short, 10<sup>18</sup> long) I don't feel safe with the ambiguity anymore.
    – zwol
    Jun 24, 2015 at 17:06
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    I've actually never seen trillion used to mean 10^18 in the U.S., though I'm aware that it's used for that elsewhere. Here, though, trillion is widely understood to mean 10^12 and it's used frequently enough that I think most people understand it without any problem.
    – reirab
    Jun 24, 2015 at 18:08
  • @MyStream The trouble comes when you impose your own definition of "count correctly" that doesn't actually match usage in English (to my knowledge, in no English-speaking country does "billion" refer to 10^12 these days). Please stop thinking about etymologies when considering what is correct; they are irrelevant. What is relevant is "what will make you understood, and what will leave people thinking you're saying something other than what you're actually saying;" in English, using "billion" to mean 10^12 is normally the latter.
    – cpast
    Jun 25, 2015 at 6:27
  • There is no right or wrong here. Both the long and the short scale are "the way counting is done" in some but not all Englishes. It is possible to cause serious confusion if you speak in one scale but your interlocutor expects the other, and that is why I suggest the use of ten-to-the-Nth for numbers larger than 10^11. Maybe I should revise that down to 10^8.
    – zwol
    Jun 25, 2015 at 13:04

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