Common measurement units and conversions

Kim is at Lina’s house. She is away and Kim promised to take care of her 2 cats - Bubbles and Alice. The cats are hungry. Lina left some instructions about how to feed the cats. The instructions say to give the cats three hundred grams of food.

Lina used a measurement of weight to say how much food Kim should prepare. We can describe mass, length, distance, or volume using standard MEASUREMENT UNITS. For example, grams are basic units we use to tell how much something weighs. Lina has a kitchen scale, so Kim can easily measure 300 grams. Alice jumped on the scales!

The scales now shows four thousand! Grams work very well for things that don’t weigh much. But it is not practical to express the mass of heavier objects in grams. There is a system which helps to express the measurements that are bigger or smaller than the basic unit. We can create new units by adding special words in front - prefixes - to the basic unit. “Deca” means “ten” so ten grams is a DECAGRAM. “Hecto” means “hundred” so a hundred grams is a HECTOGRAM. “Kilo” means “thousand” so a thousand grams is a KILOGRAM. “Deci” means “one tenth” so a tenth part of a gram is a DECIGRAM. “Centi” means “one hundredth” so a hundredth part of a gram is a CENTIGRAM. “Milli” means “one thousandth” so a thousandth part of a gram is a MILLIGRAM.

We can use the same system to describe length or distance with METRE as the basic unit or to describe volume with LITRES as the basic unit! Parts of a metre are decimetres, centimetres, and millimetres. Bigger than a metre are decametres, hectometres, and kilometres. Parts of a litre are decilitres, centilitres, and millilitres. Bigger than a litre are decalitres, hectolitres, and kilolitres.

You might not have heard of centigrams, hectometres or decalitres. Not all of these units are commonly used. But it’s good to remember these prefixes because this system makes it easier to change from one unit to another. Let’s try! Two kilometres - how many millimetres is that?

We start from kilometres and move down in our table. At each level we multiply our number by ten. One, two, three, four, five, six [!] levels. Two kilomeres is equal to... ...two million millimetres! We can also convert smaller units into bigger units.

Let’s try to convert five hundred millilitres to decilitres. We start from millilitres and move up in our table. At each level we divide our number by ten. One, Two [!] levels. Five hundred millilitres is equal to... ...five decilitres!

So, when we convert bigger units into smaller units - we multiply by ten for each level we move down. And when we convert smaller units into bigger units - we divide by ten for each level we move up. Using the same method, Kim can calculate how many kilograms Alice weighs. The scales shows four thousand grams. There are three levels between grams and kilograms and we move up...

So we have to divide by one thousand! Alice weighs four kilograms!