Square Feet Calculator
Enter length and width. A room 12 ft by 10 ft is 120 square feet.
Sources: NIST SP 811, NIST Handbook 44 Updated
Result
12 × 10 ft = 120 ft²
= 11.1484 m²
= 13.3333 yd²
= 0.00275482 ac
The formula
square feet = length × width (both in feet)
If the sides are in inches, yards, meters or centimeters, the calculator multiplies them in that unit and converts the area with the exact factor, for example 1 m² = 10.7639 ft² and 144 in² = 1 ft².
Worked example: a 12 ft by 10 ft room
- Multiply length by width: 12 × 10 = 120 square feet.
- In square meters: 120 × 0.09290304 = 11.15 m².
- In square yards, for carpet: 120 ÷ 9 = 13.33 yd².
Rooms that are not rectangles
- L-shaped room: split it into two rectangles and add the areas.
- Triangle: half of base × height.
- Circle: π × radius × radius. A round patio 10 ft across has a radius of 5 ft and an area of about 78.5 ft².
When you buy flooring or tiles, the supplier will usually tell you how much extra to add for cuts. That allowance depends on the material and the layout, so it is not built into this calculator.
Common room sizes in square feet and square meters
| Length × width | Square feet | Square meters |
|---|---|---|
| 8 ft × 10 ft | 80 | 7.43 |
| 10 ft × 10 ft | 100 | 9.29 |
| 10 ft × 12 ft | 120 | 11.15 |
| 12 ft × 12 ft | 144 | 13.38 |
| 12 ft × 15 ft | 180 | 16.72 |
| 15 ft × 20 ft | 300 | 27.87 |
| 20 ft × 20 ft | 400 | 37.16 |
| 20 ft × 30 ft | 600 | 55.74 |
Frequently asked questions
How do I calculate square feet?
Multiply the length by the width, both in feet. A room 12 ft long and 10 ft wide is 12 × 10 = 120 square feet.
My measurements are in feet and inches. How do I enter them?
Turn the inches into a fraction of a foot by dividing by 12, or type them as a fraction: 12 ft 6 in is 12.5 or 12 6/12. You can also switch “Measured in” to inches and enter 150 for 12 ft 6 in.
How do I measure an L-shaped room?
Split it into two rectangles, work out each one and add the two areas. For a room with a sloping or angled wall, split off the triangle: its area is half of base × height.
How many square feet are in a square yard?
9, because a yard is 3 feet and 3 × 3 = 9. Carpet is often priced per square yard: divide square feet by 9.
Is a square foot the same as a linear foot?
No. A linear foot is a length; a square foot is an area, a square one foot on each side. Flooring and paint coverage are sold by area, trim and fencing by length.
Sources
- NIST Special Publication 811, Appendix B.8 — 1 square foot = 0.09290304 m² exactly (checked October 12, 2026)
- NIST Handbook 44 (2026), Appendix C — 144 square inches = 1 square foot; 9 square feet = 1 square yard; 43,560 square feet = 1 acre (checked October 12, 2026)