What is a quadrillion?

The word 'quadrillion' comes from the same family of number names as 'ten', 'hundred', 'million' and 'googol'. It's just a name for a particular number.

But which number?

Another way of saying 'one quadrillion' would be 'one thousand million million'. What's that in digits? Let's work it out:

We know that 'one thousand' is written like this: 1,000 (a one with three zeroes, or 10³),

and 'one million' is written like this: 1,000,000 (a one with six zeroes or 10⁶).

So 'one thousand million' is just the 'million' bit with the 'one' replaced with 'one thousand', like this: 1,000,000,000.

So 'one thousand million million' should just be the 'million' bit with the 'one' replaced with 'one thousand million', like this: 1,000,000,000,000,000.

So 'one quadrillion' is 1,000,000,000,000,000 (a one with fifteen zeroes, or 10¹⁵).


Facts* about the word 'quadrillion'

• The SI prefix for a quadrillion is 'peta-'. This means that a 'petabyte' is one quadrillion bytes, or a 'petametre' would be a quadrillion metres.
• 'Quadrillion' can also refer to the number 'one million million million million', or 1,000,000,000,000,000,000,000,000, or 10²⁴, in the 'long scale' system of number naming. This definition is, however, falling out of use in the English language, which is why I have demonstrated the first definition in more detail (which uses the 'short scale' number naming conventions).
• The SI prefix for the long scale definition of a quadrillion is 'yotta-'. In the short scale system, 'yotta-' is the prefix for a 'septillion'.

*Whether they're interesting or not is entirely down to personal preference and circumstances.