What is square footage?
Square footage is the area of a flat surface measured in square feet: how many 1 ft × 1 ft squares would cover it. Flooring, carpet, paint, sod and home listings are all priced or described by it.
Source Common Core State Standards · Grade 3, area of rectangles (3.MD.C.7) ↗
How to calculate square feet
Here it is with your numbers:
- Multiply the length by the width: 12 × 10 = 120 sq ft.
It means you need enough flooring, paint or turf to cover 120 square feet, before any extra for waste.
For a circle, use the distance all the way across (the diameter) and halve it; for a triangle, measure the height straight up from the base, at a right angle, not along the sloping side. An odd-shaped room can be split into rectangles and the areas added.
Source Common Core State Standards · Grade 6, area of triangles (6.G.A.1) ↗Common Core State Standards · Grade 7, area of a circle (7.G.B.4) ↗
Square feet, square yards, square meters and acres
These are exact, from NIST's tables: 1 square yard is 9 square feet, 1 square foot is 0.09290304 square meters, and 1 acre is 43,560 square feet. Carpet is often sold by the square yard, so divide square feet by 9.
Source NIST Handbook 44 (2026) · Appendix C, General Tables of Units of Measurement ↗
Common room sizes in square feet
| Room | Square feet |
|---|---|
| 10 × 10 ft | 100 |
| 12 × 10 ft | 120 |
| 12 × 12 ft | 144 |
| 14 × 12 ft | 168 |
| 16 × 12 ft | 192 |
| 16 × 14 ft | 224 |
| 20 × 16 ft | 320 |
FAQs
How many square feet are in an acre?
An acre is exactly 43,560 square feet. It doesn't have to be square, but if it were, each side would be about 208.7 feet.
Source NIST Handbook 44 (2026) · Appendix C, General Tables of Units of Measurement ↗
How do you calculate square feet?
Measure the length and the width in feet, then multiply them. A room 12 feet long and 10 feet wide is 12 × 10 = 120 square feet. Change inches to feet first by dividing by 12.
Source Common Core State Standards · Grade 3, area of rectangles (3.MD.C.7) ↗
How do you work out the square feet of a room?
Measure the floor from wall to wall at its longest and widest. For an L-shaped room, split it into rectangles, work out each one and add them together.
Sources
- NIST Handbook 44 (2026): Appendix C, General Tables of Units of Measurement
- Common Core State Standards: Grade 3, area of rectangles (3.MD.C.7)
- Common Core State Standards: Grade 6, area of triangles (6.G.A.1)
- Common Core State Standards: Grade 7, area of a circle (7.G.B.4)