How to calculate square footage
Square footage is area: how many 1 × 1 ft squares fit in a space. For a rectangle it's simply length × width, measured in feet. A 12 × 10 ft room is 120 ft².
Feet and inches: convert inches to decimal feet by dividing by 12 before multiplying. 12 ft 6 in = 12.5 ft, and 10 ft 9 in = 10.75 ft, so the area is 12.5 × 10.75 = 134.4 ft². Multiplying 12.6 × 10.9 by mistake gives 137.3 ft², which is wrong.
Formulas for other shapes
| Shape | Formula | Example |
|---|---|---|
| Rectangle / square | length × width | 12 × 10 ft = 120 ft² |
| Circle | π × (diameter ÷ 2)² | 10 ft circle = 78.5 ft² |
| Half circle | ½ × π × r² | 10 ft wide = 39.3 ft² |
| Triangle | ½ × base × height | base 8, height 6 = 24 ft² |
| Trapezoid | ½ × (side a + side b) × height | (10 + 14) ÷ 2 × 8 = 96 ft² |
| Ring (around a tree) | π × (R² − r²) | R = 3 ft, r = 0.5 ft: 27.5 ft² |
| Shape | Formula | Example |
|---|---|---|
| Rectangle / square | length × width | 4 × 3 m = 12 m² |
| Circle | π × (diameter ÷ 2)² | 3 m circle = 7.07 m² |
| Half circle | ½ × π × r² | 3 m wide = 3.53 m² |
| Triangle | ½ × base × height | base 2.4, height 1.8 = 2.16 m² |
| Trapezoid | ½ × (side a + side b) × height | (3 + 4) ÷ 2 × 2.4 = 8.4 m² |
| Ring (around a tree) | π × (R² − r²) | R = 1 m, r = 0.15 m: 3.07 m² |
The calculator handles a rectangle, a circle and a triangle at once. For more shapes, run it again and add the totals, or use "Add to project".
Irregular rooms and yards
- L- and T-shaped rooms: split them into rectangles.
- Rooms with a bay window: a rectangle plus a trapezoid.
- Curved garden beds: approximate with a rectangle plus half circles, or measure the length along the middle and the average width.
- Rooms that aren't square: measure both diagonals. If they differ, the room isn't a perfect rectangle. For flooring, measuring the longest length and width covers you.
Converting units
| From | To | Multiply by |
|---|---|---|
| ft² | m² | 0.0929 |
| m² | ft² | 10.764 |
| ft² | yd² | ÷ 9 |
| yd² | ft² | 9 |
| acres | ft² | 43,560 |
| ft² | acres | ÷ 43,560 |
| hectares | m² | 10,000 |
| acres | hectares | 0.4047 |
Carpet is sometimes priced per square yard. Divide square feet by 9. The toggle above switches the whole calculator to metric.
Worked examples
L-shaped living room: 16 × 12 ft plus a 6 × 8 ft nookL-shaped living room: 4.88 × 3.66 m plus a 1.83 × 2.44 m nook
Rectangle length 16 ft · Rectangle width 12 ft · Circle diameter 0 ft · Triangle base 0 ft · Triangle height 0 ftRectangle length 4.88 m · Rectangle width 3.66 m · Circle diameter 0 m · Triangle base 0 m · Triangle height 0 m
- Total area: 192 ft²Total area: 17.8 m²
The main rectangle is 192 ft². Add the nook (48 ft²) for 240 ft². Or enter 240 × 1.The main rectangle is 17.8 m². Add the nook (4.46 m²) for 22.3 m². Or enter 240 × 1.
Patio with a round end: 12 × 10 ft rectangle + 10 ft circle (use half the circle)Patio with a round end: 3.66 × 3.05 m rectangle + 3.05 m circle (use half the circle)
Rectangle length 12 ft · Rectangle width 10 ft · Circle diameter 10 ft · Triangle base 0 ft · Triangle height 0 ftRectangle length 3.66 m · Rectangle width 3.05 m · Circle diameter 3.05 m · Triangle base 0 m · Triangle height 0 m
- Total area: 198.5 ft²Total area: 18.4 m²
- Rectangle: 120 ft²Rectangle: 11.1 m²
- Circle: 78.5 ft²Circle: 7.3 m²
Only half the circle sticks out from the rectangle, so subtract half of 78.5 ft²: 120 + 39.3 = 159.3 ft².Only half the circle sticks out from the rectangle, so subtract half of 7.29 m²: 120 + 39.3 = 14.8 m².
Gable wall for siding: 30 × 8 ft wall plus a triangle with a 30 ft base and 7.5 ft heightGable wall for siding: 9.14 × 2.44 m wall plus a triangle with a 9.14 m base and 2.29 m height
Rectangle length 30 ft · Rectangle width 8 ft · Circle diameter 0 ft · Triangle base 30 ft · Triangle height 7.5 ftRectangle length 9.14 m · Rectangle width 2.44 m · Circle diameter 0 m · Triangle base 9.14 m · Triangle height 2.29 m
- Total area: 352.5 ft²Total area: 32.7 m²
- Rectangle: 240 ft²Rectangle: 22.3 m²
- Triangle: 112.5 ft²Triangle: 10.5 m²
Where to go next
Square footage is the starting point for most material estimates. Use your total in the flooring, tile, sod or mulch calculator. Most of them accept an area if you enter it as the length with a width of 1 ft.
For real estate, "living area" follows specific measurement standards, such as ANSI Z765 in the US, which exclude garages and treat sloped ceilings in particular ways. This calculator measures plain geometric area.
Measuring tips
- Use a laser measure or a 25 ft tape, and measure twice. Record each measurement as you go on a quick sketch.
- Measure rooms wall to wall at floor level. For paint or wallpaper, measure walls and subtract openings instead.
- For big outdoor areas, a measuring wheel is faster than a tape, or use the measure tool in an online map for a rough first estimate.
- Round up to the next inch when ordering materials. Rounding down adds up across a whole room.
Common mistakes
- Multiplying feet-and-inches as if they were decimals (12 ft 6 in is 12.5 ft, not 12.6 ft).
- Using the diameter instead of the radius in π × r². That gives four times the real area.
- Adding perimeter lengths instead of multiplying for area.
- Double-counting overlapping sections when splitting an irregular shape.
Square footage in a home listing is measured differently
The area you calculate for flooring isn't the same as the "finished square footage" in a home appraisal. The ANSI Z765 standard, which Fannie Mae requires for appraisals, measures to the exterior walls and only counts finished space with at least 7 ft of ceiling height. In rooms with sloped ceilings, at least half the floor has to meet that height, and any part under 5 ft is excluded. Spaces that are partly or fully below grade are reported separately, even when finished. For a materials estimate, measure the inside of each room; for listing size, go by the standard or ask an appraiser.
Checked against
Each case below is re-run against the calculator by our automated test suite.
| Case | Our result | Checked against | Result |
|---|---|---|---|
| 12 × 10 ft rectangle plus a 10 ft circle | 198.5 ft² | Hand calculation | Match |
| Case | Our result | Checked against | Result |
|---|---|---|---|
| 3.66 × 3.05 m rectangle plus a 3.05 m circle | 18.4 m² | Hand calculation | Match |
Frequently asked questions
How do I calculate square feet with feet and inches?
Convert inches to decimal feet (inches ÷ 12), then multiply length × width. 12 ft 6 in × 10 ft = 12.5 × 10 = 125 ft².
How many square feet in an acre?
43,560.
What is the square footage of a circle?
π × radius². A 12 ft diameter circle is 113.1 ft².
How do I convert square feet to square meters?
Multiply by 0.0929.
How many square feet is a football field?
An American football field, including end zones, is 360 × 160 ft = 57,600 ft².
Sources & assumptions
The results are planning estimates, and the cost figures only use prices you enter. Product yields, densities and coverage rates vary, so check the label or ask your supplier, and follow local codes. Figures marked "approximate" or "rule of thumb" are general practice, not exact standards.
See how we calculate and test our formulas and the changelog. Last updated 2026-10-08.
Reviewed by the MaterialWhiz Editorial Team. This estimate uses the assumptions shown in the calculator. Review the result against your supplier's product coverage and site conditions. Last reviewed: October 10, 2026. See how we calculate · Report a correction.