We use special units to describe area, based on the notion of square units described ifarean this previous chapter. Because the units for length include millimetres, centimetres, metres and kilometres we end up with the following units for area.
square millimetres = mm2
(picture a square with side lengths of $1$1 mm each - pretty small this one!)
square centimetres = cm2
(picture a square with side lengths of $1$1 cm each - about the size of a fingernail)
square metres = m2
(picture a square with side lengths of $1$1 m each - what do you know that is about this big?)
square kilometres = km2
(picture a square with a side length of $1$1km - I wonder how many of these your town or city's land area measures?)
When converting units of area we need to work out how many smaller square units fit into the larger square unit. This applet can help us to visualise and understand this conversion. Have a look at the different conversions shown here by sliding the slider.
Converting into square metres: $1000\times1000$1000×1000 m2 = $1000000$1000000m2
What if we want to turn $1$1 km2 into cm2 (square centimetres)?
First we would have to work out how many centimetres are in a length of one kilometre:
$100$100 (centimetres in each metre) × $1000$1000 (metres in each kilometre) =$100000$100000.
Then we multiply the side lengths of the square kilometre: $100000\times100000=10000000000$100000×100000=10000000000cm2. WOAH this is huge! This is exactly why we use different units of area. Imagine having to describe the size of your classroom in square centimetres.
Converting into square centimetres: $100\times100=10000$100×100=10000 cm2
Converting into square millimetres: $1000\times1000=1000000$1000×1000=1000000 mm2
Converting into square millimetres: $10\times10=100$10×10=100 mm2
When measuring land there are two other common units of area.
hectare = ha
$1$1 ha = $10000$10000m2
(imagine a square $100$100 m x$100$100 m - this is the size of a hectare)
An acre is a very common unit for measuring blocks of land here in Australia, UK and indeed a lot of countries around the world. But $1$1 acre has a very bizarre conversion.
$1$1 acre =$4046.85642$4046.85642 m2. Quite a bizarre number really, especially when all the numbers we have used so far in our conversions are multiples of $10$10 and nice to work with.
In fact an acre is an imperial unit, where $1$1 acre = $4840$4840 square yards. Whilst still not a multiple of $10$10 (like the units in our metric system are), it is still a lot nicer than $4046.85642$4046.85642 m2.
Fortunately for us as budding mathematicians it is not common to convert between acres and metric measurements.
Express $10.4$10.4ha in m2.
Convert $34000$34000cm2 to m2.
A rectangular farm has an area of $12$12 ha and a length of $600$600 m. What is the width of the farm in metres?
Apply the relationships between units in the metric system, including the units for measuring different attributes and derived measures
Apply measurement in solving problems