How to write large numbers
Every large number in English is groups of three digits, each but the last with a scale word after it. Once you have the list of scale words, there is nothing else to learn.
The groups of three
English counts in threes. Mark a long number off in groups of three digits from the right, then read the groups from the left, saying each as an ordinary number under a thousand followed by its scale word. The last group, the units, takes no scale word. That is the whole system, and it is why the commas in 1,500,000 sit where they do: they mark the group boundaries, which is also where the name changes.
A group of zeros is simply skipped. 2,001,000 is “two million one thousand”, with nothing said about the empty units group at all.
The scale words
Each is a thousand times the one above it.
| Word | Zeros | Written out |
|---|---|---|
| thousand | 3 | 1,000 |
| million | 6 | 1,000,000 |
| billion | 9 | 1,000,000,000 |
| trillion | 12 | 1,000,000,000,000 |
| quadrillion | 15 | 1,000,000,000,000,000 |
| quintillion | 18 | 1,000,000,000,000,000,000 |
| sextillion | 21 | 1,000,000,000,000,000,000,000 |
| septillion | 24 | 1,000,000,000,000,000,000,000,000 |
| octillion | 27 | 1,000,000,000,000,000,000,000,000,000 |
| nonillion | 30 | 1,000,000,000,000,000,000,000,000,000,000 |
| decillion | 33 | 1,000,000,000,000,000,000,000,000,000,000,000 |
Past a decillion the names stop being settled. Several systems exist for continuing, none is in general use, and a number that large is written in scientific notation. The converter stops at thirty-six digits for that reason.
Worked examples
| Number | In words |
|---|---|
| 1,000 | one thousand |
| 10,000 | ten thousand |
| 100,000 | one hundred thousand |
| 1,000,000 | one million |
| 1,500,000 | one million five hundred thousand |
| 1,000,000,000 | one billion |
Scale words never take an s
When a scale word follows a number it stays singular: two million people, never two millions. The plural only appears when the word is used loosely as a noun with “of” after it, as in “millions of people” or “thousands of years”, where no specific number is being given.
Where the commas go in the digits
Every three digits from the right, and never in a year, a page number, a house number or a postcode. Four-digit numbers are the borderline: 1500 and 1,500 are both normal, and the comma is usually dropped in a year and kept in an amount.
Some technical and international styles use a thin space instead of a comma (1 500 000) to avoid a clash with the decimal comma used across much of Europe. Either is unambiguous as long as the document keeps to one.
Billion is the one to check
A billion means a thousand million here and in all modern English usage. It has not always, and older British sources use it to mean a million million. The long and short scale explains which documents are affected and how to tell.