Converting units

Hello, and welcome to Myriora Maths! A race is one point five kilometres long. How many metres is that? Changing units is easy, once you know two things: how many, and which way. Let's see.

Here are the facts to know. A thousand metres make a kilometre. A hundred centimetres make a metre. Ten millimetres make a centimetre. And a thousand grams make a kilogram, and a thousand millilitres make a litre.

Going from a big unit to a small unit, you need more of them, so multiply. One point five kilometres, times a thousand, is one thousand five hundred metres.

Going from a small unit to a big unit, you need fewer of them, so divide. Two thousand five hundred grams, divided by a thousand, is two point five kilograms.

Always ask: should the number get bigger or smaller? Small units make big numbers. Big units make small numbers.

Let's try one together. How many metres are in four kilometres? Say it out loud!

Kilometres to metres, so multiply by a thousand. Four thousand metres!

Here's a question that catches lots of people. What is two point five metres in centimetres? Some people say twenty-five centimetres. But a metre is a hundred centimetres, so two and a half metres is two hundred and fifty centimetres. Times by a hundred, not ten!

Your turn! What is three point two kilograms in grams? Pick the right card. You've got twenty seconds, or pause the video. Go!

Time's up! Kilograms to grams: multiply by a thousand. Three point two times a thousand is three thousand two hundred grams!

Quick review. Know the facts: a thousand, a hundred, or ten. Big unit to small unit: multiply. Small unit to big unit: divide. And check whether the number should get bigger or smaller. See you next time!