How to calculate square footage
Square footage is the area of a flat surface: how many 1 × 1 ft squares it would take to cover it. For a rectangle, multiply length by width. Other shapes have their own formulas, and anything irregular can be split into those basic shapes and added up.
L-shape = (length A × width A) + (length B × width B)
Triangle = ½ × base × height
Circle = π × (diameter ÷ 2)², or about 0.7854 × diameter²
Measure in feet and the answer is in square feet. If you measured in another unit, convert the result:
Square yards × 9 = square feet
Square meters × 10.764 = square feet
Worked examples
- Bedroom, 12 ft 6 in. × 11 ft. Convert 6 in. to 0.5 ft, so the length is 12.5 ft. Area: 12.5 × 11 = 137.5 sq ft, or 15.28 sq yd (137.5 ÷ 9).
- L-shaped living room. Split it into a 20 × 12 ft main area and an 8 × 10 ft alcove. Area: 240 + 80 = 320 sq ft, or 35.56 sq yd.
- Round patio, 12 ft across. Radius is 6 ft. Area: 3.1416 × 6 × 6 = 113.1 sq ft.
- Triangular garden bed with a 12 ft base and 8 ft height: ½ × 12 × 8 = 48 sq ft.
- Measured in inches: a 150 × 132 in. room is 19,800 sq in. Divide by 144: 137.5 sq ft.
How to measure a room
- Use a 25 ft tape measure or a laser measure. Measure wall to wall at floor level, and take the longest dimension in each direction.
- Write measurements in feet and inches, then convert the inches to decimal feet before multiplying (see the table below). Multiplying 12'6" as "12.6" is a common mistake that undercounts the area.
- Round up to the nearest inch. For materials, a little extra is better than a little short.
- Include closets and alcoves if the flooring continues into them. Skip spaces under permanent cabinets or a kitchen island if the floor won't run under them.
- For walls (paint, drywall, wallpaper), measure the wall width and ceiling height instead of the floor. The paint calculator and drywall calculator handle doors and windows.
| Inches | 1 | 2 | 3 | 4 | 6 | 8 | 9 | 10 |
|---|---|---|---|---|---|---|---|---|
| Decimal feet | 0.083 | 0.167 | 0.25 | 0.333 | 0.5 | 0.667 | 0.75 | 0.833 |
Irregular rooms and spaces
Almost any floor plan can be broken into rectangles. Sketch the room, draw lines to divide it into rectangles that don't overlap, measure each one and add them. For an L-shaped room, that's two rectangles; for a T or U shape, three.
- Cutouts: calculate the full rectangle, then subtract the piece that's missing, such as a chimney or a stair opening.
- Angled walls: treat the angled corner as a triangle and add or subtract it.
- Curved edges: a half circle is half the circle area. For freeform garden beds, a rough rectangle that covers the shape is usually close enough for buying mulch or sod.
Area conversion table
| Unit | Equals |
|---|---|
| 1 square inch | 0.00694 sq ft · 6.4516 cm² |
| 1 square foot | 144 sq in · 0.1111 sq yd · 0.0929 m² |
| 1 square yard | 9 sq ft · 1,296 sq in · 0.8361 m² |
| 1 square meter | 10.764 sq ft · 1.196 sq yd |
| 1 acre | 43,560 sq ft · 4,840 sq yd · about 4,047 m² |
Common room sizes
| Room size | Square feet | Square yards | Square meters |
|---|---|---|---|
| 10 × 10 ft | 100 | 11.11 | 9.29 |
| 10 × 12 ft | 120 | 13.33 | 11.15 |
| 12 × 12 ft | 144 | 16 | 13.38 |
| 12 × 15 ft | 180 | 20 | 16.72 |
| 14 × 16 ft | 224 | 24.89 | 20.81 |
| 20 × 20 ft | 400 | 44.44 | 37.16 |
Square feet vs. square yards
A square yard is 3 ft × 3 ft, or 9 sq ft. Carpet was traditionally priced by the square yard, and some installers and quotes still use it, while most flooring today is priced per square foot. To compare, divide a per-square-yard price by 9: $27 per sq yd is the same as $3 per sq ft.
Carpet also comes off rolls, commonly 12 ft wide. Because of roll width, seams and pile direction, you often need more carpet than the room's raw area suggests, so get the installer's measurement before you buy.
A note on home square footage: the figure in a real estate listing usually follows a measurement standard (many appraisers use ANSI Z765), which measures finished, above-grade space from the exterior walls. It won't match the sum of your room measurements, and that's expected.
What to do with your square footage
- Flooring and tile: buy by the box with 5–15% extra for cuts. See the flooring calculator and tile calculator.
- Lawns and patios: sod is sold by the square foot and pallet; pavers by the piece or square foot. Try the sod calculator and paver calculator.
- Bulk materials: mulch, gravel, topsoil and concrete need a depth, too. Area × depth gives volume; the cubic yards calculator, mulch calculator and concrete calculator do that step.
- Roofing: shingles are sold by the "square," which is 100 sq ft of roof. The roofing calculator accounts for pitch.
Frequently asked questions
How do I calculate the square footage of a room?
Measure the length and width in feet and multiply them. A room that is 12 feet by 15 feet is 12 × 15 = 180 square feet. For an L-shaped or irregular room, split it into rectangles, calculate each one and add them together.
How many square feet is a 12×12 room?
A 12×12 room is 144 square feet, which equals 16 square yards or about 13.38 square meters.
How do I convert square feet to square yards?
Divide by 9, because a square yard is 3 feet by 3 feet. For example, 180 square feet ÷ 9 = 20 square yards. To go the other way, multiply square yards by 9.
How do I calculate square feet from inches?
Multiply the length and width in inches to get square inches, then divide by 144. A 30 × 48 inch area is 1,440 square inches, which is 10 square feet.
How many square feet are in an acre?
One acre is 43,560 square feet, or 4,840 square yards. A square acre measures about 208.7 feet on each side, and a quarter-acre lot is 10,890 square feet.
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