Thousand, Million, Billion

The Sun is about 150 million kilometres away. More than 8 billion people live on the Earth. Numbers like these appear in the news, in science and in every measurement of the sky. But what do "million" and "billion" really mean, and how do you write them?

Three zeros at a time

You already know a thousand: 1,000, a 1 followed by 3 zeros. In the Bigger Than a Metre lesson we saw that 1,000 metres make a kilometre.

Now take a thousand thousands. In the Moving the Point lesson we saw that multiplying by 1,000 means adding three zeros. So a thousand thousands is 1,000,000: a 1 followed by 6 zeros. That is a million.

Take a thousand millions, and add three more zeros: 1,000,000,000, a 1 followed by 9 zeros. That is a billion.

thousand = 1,000 (3 zeros)
million = a thousand thousands = 1,000,000 (6 zeros)
billion = a thousand millions = 1,000,000,000 (9 zeros)

Each step is a thousand times the one before.

The commas help

Look at where the commas go: one after every three digits, counting from the right. Each comma is a step of a thousand. So you can read a big number by its groups:

1 group of three after the first digits: thousands;
2 groups: millions;
3 groups: billions.

The number 8,200,000,000 split into groups of three digits by commas. Counting from the right: ones, thousands, millions, billions. So it reads 8 billion 200 million

So 150,000,000 has two groups of three after the 150: that is 150 million. And 8,200,000,000 has three groups after the 8: that is 8 billion, 200 million, or 8.2 billion.

In words and numbers

News and science often mix the two: "150 million km" is easier to read than "150,000,000 km", and it means exactly the same. When you see one, you can now write the other.

(Some languages have their own words for these numbers. In Persian, French and German, for example, a thousand millions is a "milliard".)

Try it at home

Write these as numbers with commas: two million; forty thousand; three billion.
Read these aloud: 7,000,000; 25,000; 1,500,000,000.

Answers: 2,000,000; 40,000; 3,000,000,000. Seven million; twenty-five thousand; one billion, five hundred million (or 1.5 billion).

Words to know

million - a thousand thousands: 1,000,000
billion - a thousand millions: 1,000,000,000

Big idea

A thousand has 3 zeros, a million 6 and a billion 9. Each is a thousand times the one before, and the commas, one every three digits, show you which one you are reading.