Square Inch (in²)
The square inch, or in², is the smallest commonly used unit of area in the imperial system. It is the area of a square with one-inch sides and equals 6.4516 square centimeters. It originates from the inch and has been widely used in engineering, technical drawings, and manufacturing. Today, it is still good for small things like screens, machine parts, and prints. Most countries now use square centimeters, but the square inch is still used in areas where the imperial system is prevalent.
Acre (ac)
The acre, or ac, is a unit of area used in the imperial and US systems. It originated in medieval England and referred to the land a team of oxen could plow in a day. Today, one acre is 4,840 square yards or 4,046.856 square meters. Acres are still used in the US, Canada, and the UK for real estate, land sales, and farms. While the metric system is more common worldwide, the acre is still used because it is part of tradition and is easier to use in daily life.