The square inch equals 6.4516 square centimetres exactly. Used in US engineering, tile specifications, stamp areas and pressure conversion (PSI = pounds per square inch). A US letter-size sheet is 93.5 in².
Real-world: A US letter page is 93.5 in². A common US tile is 144 in² (1 ft²). Credit card ≈ 7.1 in².
Read full square inch reference →The acre equals 4046.86 square metres — originally the area a team of oxen could plough in a day. It is the standard rural land unit in the US, UK and Canada. Suburban American lots are typically a quarter to half an acre. 640 acres equal one square mile.
Real-world: A US suburban lot is 0.25–0.5 acre. A standard UK rural property might be 5 acres. A football pitch is about 1.8 acres.
Read full acre reference →