US Standard Area
These are the most common measurements:
 Square Inch
 Square Foot
 Square Yard
 Acre
 Square Mile
Small surfaces are usually measured in square inches, rooms and buildings in square feet, carpet in square yards, property in acres, and territory in square miles.
Square Inch
Area is length by length, so a square inch is a square that is 1 inch on each side.
The Unit is inch × inch, which can be written many ways, such as:
 in^{2}
 inch^{2}
 sq in
 sq inch
 square inch
 etc ...
Square Foot
A square foot is a square that is 1 foot on each side.
Here Ariel the Dog sits next to a square foot made with tape measures.
The Unit is foot × foot, which can be written many ways, such as

Square Yard
A square yard is a square that is 1 yard on each side. It is equal to 9 square feet.
Acre
One acre is equal to 43,560 square feet.
It is roughly equal to a football field in area.
It is exactly the area 66 ft by 660 ft.
Or 198 ft by 220 ft.
Acres are commonly used to measure land.
Square Mile
A square mile is a square that is 1 mile on each side.
Square miles are commonly used to measure large areas of land.
More Examples
A square inch is about:
 6½ square centimeters
An acre is:
 4,840 square yards
 43,560 square feet
 4,046.8564224 square meters
 a square with sides about 208.71 feet (or 69.57 yards)
 about 0.4 hectare (40% of the area of a hectare)
 a bit less than a football field
 about 16 tennis courts
A square mile is:
 640 acres