So how do we convert between the different SI units for length?
People often get confused with this, especially when it comes to area and volume unit conversions.
In this video I’ll teach you a couple of simple tricks to help you to get it right
every time.
Here are the basic metric units for length.
There are ten millimetres in a centimetre, and a hundred centimetres in a metre, which
makes a thousand millimetres in a metre.
Milli- means one thousandth, and centi- means one hundredth.
There are also a thousand metres in a kilometre.
Kilo- means one thousand.
You have to know these prefixes.
But when it comes to converting measurements, when do you multiply and when do you divide?
Here’s the first trick: If the new unit is smaller, you need more of them, so multiply.
If the new unit is larger, you need less of them, so divide.
Let’s try a few.
Forty-two millimetres is how many centimetres?
Well, there are ten millimetres in a centimetre, and centimetres are bigger than millimetres,
so I need less of them: divide.
Forty-two divided by ten is four point two centimetres.
Twelve thousand and fifty metres is how many kilometres?
Well, there are one thousand metres in a kilometre, and kilometres are bigger than metres, so
I need less of them: divide.
Twelve thousand and fifty divided by one thousand is twelve point zero five kilometres.
Four kilometres is how many metres?
There are a thousand metres in a kilometre, and metres are smaller than kilometres, so
I need more of them: multiply.
Four times one thousand is four thousand metres.
One point six metres is how many millimetres?
There are one thousand millimetres in a metre, and millimetres are smaller than metres, so
I need more of them: multiply.
One point six times one thousand is one thousand six hundred millimetres.
Let’s try a few two-step conversions.
Eight point three centimetres is how many kilometres?
Well, there are one hundred centimetres in a metre, and then one thousand metres in a
kilometre, so that makes one hundred thousand centimetres in a kilometre.
Kilometres are bigger than centimetres, so I need less of them: divide.
Eight point three divided by one hundred thousand is zero point zero zero zero, zero eight three
kilometres.
One more.
Thirty-one kilometres is how many millimetres?
Well, there are a thousand millimetres in a metre, and then a thousand metres in a kilometre,
so that makes a thousand times a thousand, or one million millimetres in a kilometre.
Millimetres are smaller than kilometres, so I need more of them: multiply.
Thirty-one times one million makes thirty-one million millimetres.