How to calculate square footage
For a rectangular room or lot, multiply the length by the width, both measured in feet.
Square feet = length × width
A room 12 feet by 15 feet is 12 × 15 = 180 square feet.
Other shapes
| Shape | Formula |
|---|---|
| Rectangle | length × width |
| Triangle | base × height ÷ 2 |
| Circle | 3.1416 × radius × radius |
| L-shaped room | split into two rectangles and add them |
Measuring in inches
If a measurement includes inches, turn them into a decimal of a foot by dividing by 12. A wall 10 feet 6 inches long is 10.5 feet.
Square footage of a house
Measure each room, work out its area and add the results. Listings usually count finished, heated living space only. Garages, unfinished basements and porches are normally left out.
How to use this calculator
Choose a shape (rectangle, triangle or circle), then enter the length and the width of the room, house or lot. For a circle, the length is the diameter, which is the full distance across. The square footage calculator shows the area in square feet and also in square yards, square meters and acres. You can enter the number of areas of that size and a price per square foot as well. For any other shape, split it into simple shapes, calculate each one and add the answers.
More examples
- L-shaped room. Split it into a 12 by 15 foot rectangle and an 8 by 10 foot rectangle. 180 + 80 = 260 square feet.
- Triangle. A corner with a base of 10 feet and a height of 8 feet is 10 × 8 ÷ 2 = 40 square feet.
- Circle. A round patio with a radius of 6 feet is 3.1416 × 6 × 6 = about 113.1 square feet. The radius is half the distance across.
- Feet and inches. A room 10 feet 6 inches by 12 feet 3 inches is 10.5 × 12.25 = about 128.6 square feet.
What the result means in other units
The 180 square foot room from the first example converts like this:
| Unit | How to convert | 180 sq ft equals |
|---|---|---|
| Square yards | divide by 9 | 20 sq yd |
| Square meters | multiply by 0.092903 | 16.72 m² |
| Acres | divide by 43,560 | 0.0041 acres |
Using square footage to buy materials
Floor area tells you how much flooring to order. Add about 10% for a straight layout and about 15% for a diagonal or herringbone layout. For the 180 square foot room that is 198 square feet or 207 square feet.
Paint is different, because you are covering walls and not the floor. Measure each wall’s length times its height. One gallon of paint covers about 350 to 400 square feet.
What changes the result
- Where you measure. Measure wall to wall at floor level. Baseboards and trim can take an inch or two off a reading taken higher up.
- Closets and alcoves. Add them if the material goes there. Leave them out if it does not.
- Rounding. Rounding each measurement up to the next foot can add several square feet to a small room. Use inches for a closer answer.
Common mistakes
- Multiplying feet by inches without converting first. 10 feet 6 inches is 10.5 feet, not 10.6.
- Using the distance across a circle in place of the radius.
- Forgetting to divide by 2 for a triangle.
- Measuring an L-shaped room as one large rectangle.
- Ordering material for the exact area with nothing extra for cuts.
Related calculators
Take your area straight into the flooring calculator or the paint calculator to get quantities. For land, the acreage calculator works in acres, and the square feet to square meters converter handles metric plans.
Frequently asked questions
How many square feet is a 10 by 10 room?
10 × 10 = 100 square feet.
How many square feet is a 12 by 12 room?
12 × 12 = 144 square feet.
How do I convert square feet to square yards?
Divide by 9. Carpet is often sold by the square yard. See the square feet to square yards converter.
How much extra material should I buy?
For flooring and tile, add about 10% for cuts and waste. Add more for diagonal layouts.
How many square feet is a 20 by 20 room?
20 × 20 = 400 square feet.
How do I find the square footage of a wall?
Multiply the wall’s length by its height. A wall 12 feet long and 8 feet high is 96 square feet.
How many square feet are in an acre?
One acre is 43,560 square feet.
What is the difference between square feet and linear feet?
Linear feet measure length only. Square feet measure area, which is length times width.