Metric measurements
Metric measurements of area are widely used around the world due to their simplicity and consistency. The metric system employs the square meter (m²) as the base unit for measuring area. This unit is derived from the meter, which is the base unit for measuring length. The square meter represents the area of a square with sides measuring one meter.
For larger areas, metric prefixes are used to indicate multiples or fractions of the square meter. For example, the hectare (ha) is commonly used to measure land areas. One hectare is equal to 10,000 square meters, or 100 meters by 100 meters. This unit is often used in agriculture and urban planning.
For smaller areas, the square meter can be divided into smaller units using metric prefixes. The most commonly used subunits are square centimeters (cm²) which is equal to a ten thousandth of a square meter, and square millimeters (mm²) which is one millionth. These units are often used in scientific and engineering applications where precise measurements are required.
Imperial / American measurements
Imperial or American measurements of area are commonly used in the United States and a few other countries that have not adopted the metric system. These measurements are based on the foot, which is divided into inches, and the yard, which is composed of three feet. The most commonly used units of area in this system are square inches, square feet, square yards, and acres. The Old English word "acre" means field and it was generally considered the area that could be ploughed in a day using a yoke or oxen.
The square inch is used for small-scale measurements, such as the size of a postage stamp or the area of a small object. The square foot is a larger unit and is commonly used to measure the area of rooms in houses or apartments. The square yard is even larger and is often used to measure the area of outdoor spaces, such as lawns or gardens. Finally, the acre is the largest unit of area in this system and is commonly used to measure the size of large plots of land, such as farms or estates.
While the metric system is widely used around the world, Imperial or American measurements of area continue to be used in certain contexts, particularly in the United States and sometimes in the United Kingdom.
Converting between metric and imperial area measurements
Square the length factor. A metre is about 3.28084 feet, so a square metre is 3.28084 × 3.28084, which comes to about 10.764 square feet. Going back, a square foot is exactly 0.09290304 m², because a foot is exactly 0.3048 m.
So a 20 m² room is about 215 sq ft. The classic mistake is multiplying by 3.28 and stopping there, which makes the room come out at under a third of its real size.
An acre is exactly 4,046.8564224 m², a shade over 0.4 hectares.