Overview
A square foot is a unit of area in the imperial and United States customary systems. It is defined as the area contained within a square whose sides are each one foot long. The symbol often used is ft2 or sq ft. The concept is simple and widely used in everyday measurements of floors, walls, plots of land and building plans.
Definition and conversions
Because one foot equals 0.3048 metres by international agreement, a square foot equals exactly 0.09290304 square metres. In customary units it equals 144 square inches. In terms of larger land measures, one square foot is 1/43,560 of an acre. Common conversions used in practice include:
- 1 sq ft = 144 sq in
- 1 sq ft = 0.09290304 m2
- 1 acre = 43,560 sq ft
Uses and examples
Square feet are most familiar in building and real estate contexts: floor area, carpet sizes, paint coverage estimates and heating/cooling load calculations are often quoted in square feet. For example, a room measuring 10 feet by 12 feet has an area of 120 square feet (10 × 12 = 120). Floor plans, rental listings and construction specifications in the United States commonly present dimensions and areas in square feet.
History and regional practice
The square foot derives directly from the foot, a unit with ancient origins. Its modern value follows the 20th-century international agreement that fixed the international foot at exactly 0.3048 metres. While the metric system is dominant globally, the square foot remains the primary area unit for many trades and industries in the United States and is also used to varying degrees in other countries and territories for real estate and construction.
Notes and resources
When precise metric-area values are required, convert square feet to square metres using the exact factor above. For further technical definitions and standards, see primary unit definitions.
Quick reference
- Symbol: ft2 or sq ft
- One square foot: area of a 1 ft × 1 ft square
- Common contexts: housing, commercial real estate, interior design, construction