I guess if I say

one hundredth

people would probably easily know what I mean, it is equal to 0.01, 1% or 1/100.

Although I am not sure whether I said it correctly.

How about 1/1,000,000,000,000,000?

I don't even know how to call the "1,000,000,000,000,000" part before I google it.

I guess most of us don't know how many zeros are in a quadrillion before looking it up.

So, I am afraid directly call that thing "one quadrillionth" is not a good idea, especially in speaking. What would I refer to it?

How about "one million billionth", as google knows it?

Could someone please give a hint? Thanks in advance.

  • Google shows different results to different people. Why do you need to say "one quadrillionth"? What's your use case? – CJ Dennis Apr 1 at 23:57

The easy way to handle such numbers is with scientific notation.
Wikipedia "scientific notation"

Taking your first example, "1/1,000,000,000,000,000", start with the inverse,
1,000,000,000,000,000. There are 15 zeros. That number is expressed as 1.0 x 10^15.
When you divide one by that number, the exponent 15 becomes negative, and it is called 1.0 x 10^-15.

Now, there's an orderly way to name such numbers starting with 1000, and going in factors of 1000.
So, 1000 = 1.0 x 10^3
1 million = 1.0 x 10^6
1 billion = 1.0 x 10^9
1 trillion = 1.0 x 10^12
1 quadrillion = 1.0 x 10^15,
and so on for quintillion, sextillion, septillion, octillion, nonillion, and that's all I know.
But these names of numbers aren't very useful because they are very uncommon. If you stick with scientific notation, it's easy to get a mental picture of the number and to do arithmetic with it.

(Note that these names of number apply in the US. There may be other places that use a different system.)

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  • Thank you so much. scientific notation is a good way to refer to a large number in writing. How about in speaking? – WXJ96163 Apr 1 at 5:50
  • Try saying "one times ten to the fifteenth" or "one times ten to the minus fifteenth". It's easy, and it will be understood faster and better than "one quadrillion" or "one quadrillionth" by most technical people. There is also the option of "metric prefixes" (check Wikipedia for that) to express very large and small quantities. You may have heard of "petabytes" or "femtoseconds". – Jack O'Flaherty Apr 1 at 5:58
  • Thank you. I guess that is what I am look for, although I don't even know its name. Does "ten to the fifteenth" refer to "ten to the power of negative fifteen". – WXJ96163 Apr 1 at 6:02
  • No, check the articles I mentioned. Ten to the fifteenth is a very large number, while ten to the power of negative fifteen is a very small one. In fact, the first number is ten to the thirtieth times larger than the second. The only problem with the metric prefixes is that you attach them to a unit, like "second" or "byte", and they don't work for simple numbers. – Jack O'Flaherty Apr 1 at 6:07
  • Actually, I'd like to attach the number to "second" to explain the concept of femtosecond in speaking. That's why I asked my OP. – WXJ96163 Apr 1 at 8:26

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