Why Do We Count in Tens?

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We count in tens.

10s, 100s, 1000s...

Our numeric system is based on multiples of 10.

We see this at work in many places.

There are 10 millimetres in a centimetre.

100 centimetres in a metre.

And 1000 metres in a kilometre.

It's called the decimal system and the prefix dec – is Latin for ten.

The decimal system

But why 10? Why not 12, or 18?

Base Systems

The number of units in a counting system is known as the 'base'.

Our decimal system uses ten numbers – 0 to 9 – so it's a base 10 system.

You also use another base system on a daily basis: to tell the time.

There are 60 seconds to a minute.

And 60 minutes to an hour.

So time uses a base 60 system.

In fact, 60 is a much better base than 10, because it can be divided up more easily.

10 can only be divided exactly by itself, 5, 2 and 1.

But 60 can be divided exactly by itself, 30, 20, 15, 12, 10, 6, 5, 4, 3, 2 and 1.

This makes it a much more useful number for a base system.

So why have we ended up with base 10?

Before most people could write, they used their bodies to count.

Historical drawings show that body parts were used to count in many cultures.

An example is the Yupno from Papua New Guinea, who use different body parts, each representing different numbers...

Yupno Tribe
Papua New Guinea

Starting with the fingers and toes and then moving to your ears, eyes and nose!

But to avoid doing a complicated dance every time you went to the shops, using tens – counted easily on your fingers – made sense.

10s became 100s, and 100s became 1000s...

All numbers which can be represented using 10 digits.

If we had 12 or 18 fingers, we might organise the world in a very different way!