The standard unit of area in the metric system is the square meter (m²), with square centimeters (cm²) for smaller areas and square kilometers (km²) for larger ones. Area is length times length, so each is the square of the matching length unit.
In the imperial or English system of measurements, area is typically expressed in square units such as square inches, square feet, square yards, or acres. Converting between different units of area in the imperial system can be done by understanding the relationships between the units.
Going from a larger unit to a smaller one, multiply by the conversion factor; going back, divide. The catch is that the factor is squared – a meter is 100cm but a square meter is 10,000cm².
For example, to convert square feet to square yards, you can divide the number of square feet by 9, as there are 9 square feet in 1 square yard.
To convert square yards to acres, divide by 4,840 – 9,680 square yards is 2 acres. Going the other way, multiply.
Hectares
A hectare is 10,000 square meters, or about 2.47 acres. A small farm might be a few hectares and a large commercial one hundreds.
To convert hectares to acres one must multiply by 2.47105.
Acres
An acre is 43,560 square feet, which is about 4,047 square meters. 640 acres make a square mile.
An acre was traditionally the area a yoke of oxen could plough in a day, later fixed as a strip one furlong by one chain (220 yards by 22 yards). The United States and the United Kingdom still use it for land, while most other countries use the hectare. To convert acres to hectares, multiply by 0.4047.
Square meters
A square meter (m²) is the area of a square one meter on each side, and in most countries it is the unit for the floor area of rooms and houses.
When converting from square meters to square feet, it is important to keep in mind that the relationship between square meters and square feet, for example, is not the same as that of meters to feet. One square meter is equal to approximately 10.76 square feet.
A 20 square meter room is 215.2 square feet (20 × 10.76). For a rough figure multiply by 10 and add 8%, which gets you 216.
Square feet
A square foot is the area of a square one foot on each side, which is 144 square inches or about 0.0929 square meters. It is the usual unit for floor and property areas in the United States.
When converting square feet to square meters, you need to divide the square feet value by 10.76.
A room 10 feet by 12 feet is 120 square feet, which is about 11.15 square meters (120 ÷ 10.76).