2.4 Unit Conversion It is important that you understand how to express of the same quantity in different units.
You can use different units depending on what you want to express and measure. A house’s size can be expressed in square meters. Imagine if you would like to express the area of a house in square millimeters or square kilometers intead:
How big is a house which is 63,000,000 mm^{2}?
How big is a house which is 0.000082 km^{2}?
It would be very hard to answer. Right?
In the picture, a square with a side of 1 m is shown. The figure’s area is:
1 m · 1 m = 1 m^{2} 


If we instead give the measurement in dm, then the side’s length is 1 m = 10 dm.
The figure’s area calculated in dm^{2} is:
10 dm · 10 dm = 100 dm^{2} 


With the example above, we have shown that 1 m^{2} is the same thing as 100 dm^{2}.
We continue and indicate the units in cm. The side’s length is 1 m = 100 cm.
The figure’s area is calculated as:
100 cm · 100 cm = 10,000 cm^{2} 


1 m 
= 
10 dm 
= 
100 cm 
1 m^{2} 
= 
100 dm^{2} 
= 
10,000 cm^{2} 
Geographic areas often use different units. Two units that are sometimes used are acres in the Imperial System or hectars in the Metric.
1 hectare = 100 acre = 10,000 m^{2}
