Area is the measure of how much space something takes up on the ground, floor, wall or other flat surface. Note that by flat we do not mean totally flat, as a ball has a surface area too, just that we mean flat as in not measuring the thickness as well, as that is covered by volume.
If we measure something simple and small, such as a small rectangle, and we get a ruler, and one side we measure as 7 centimetres and one side as 14 centimetres, we can calculate the area by multiplying the two numbers together, to get 7 × 14 = 98 cm^{2}.
If you want to measure the area of the floor of a square or rectangular room in a house, then you would get a tape measure and measure the distance between two opposite walls, then the distance between the other two opposite walls, and multiply the distances to get the area. If you measure the distances in metres, then the area will be in square metres, which is also written as m². Therefore, if you measure the room and one distance is 4 metres, and the other is 3 metres, then the area is 4 × 3 = 12 m².
For measuring larger areas, such as the size of land, we can use hectares, which is 100 ares (as hect prefix, sometimes hecto, means 100 of a unit, see Principles for definitions of metric prefixes). 1 are (pronounced air) has an area of 100 m². That is, an area of 1 are, if it were an exact square on the ground of land, would have a length of 10 metres on each side, as 10 metres multiplied by 10 metres gives 100 m² (10 × 10 = 100). But as this is a fairly small area, for measuring land areas a larger unit is more commonly used, which is 100 ares, known as a hectare. 1 hectare has an area of 100 m × 100 m = 10 000 m², i.e. ten thousand square metres, which would be equivalent to an area of land, if a perfect square, having each side equal to 100 metres.
If we are measuring the areas of much larger places, such as cities and countries, we can use square kilometres, written as km².
If we are measuring much smaller areas, such as the area of a table top, we could use square centimetres, written as cm². One square metre is 10 000 cm². One metre in length is 100 centimetres, so you might think that one square metre is 100 square centimetres. But, as we are dealing with area, and everything is in square units, therefore going from one unit to a larger unit of area, we have to square the length, i.e. 100 cm in 1 metre, but a square metre is 100² = 100 × 100 = 10 000 cm².
If we are going to measure a table top, for example, measure the length and width in centimetres, for example it might be 120 cm by 50 cm. So the area is simply 120 × 50 = 6000 cm². This could also be expressed as 0.6 m² (as there are 10 000 cm² in 1 m²).
Place areas
Place  Area in km²  Area in hectares 
United Kingdom  244 820  24 482 000 
Great Britain (source)  234 410  23 441 069 
England  132 588  13 258 845 
Scotland  80 233  8 023 382 
Wales  21 588  2 158 842 
Northern Ireland  10 411  1 041 100 
Greater London, UK  1 579  157 900 
City of London  3  290 
Australia  7 686 850  
United States of America  9 629 091  
Canada  9 976 140  
Europe (including UK)  10 400 000  
South America  17 818 508  
North America  24 230 000  
Africa  30 244 050  
Asia  49 694 698 

Surface area of the Earth  510 067 420 

