Square Footage Calculator
Add one area per row, rectangle, triangle or circle, and get the total in square feet, plus square yards, square meters and acres. Lengths accept feet and inches, like 12 ft 6 in.
Area is computed one shape at a time, then added. Rectangle: length × width. Triangle: ½ × base × height. Circle: π × (diameter ÷ 2)². Divide square feet by 9 for square yards or by 43,560 for acres.
Example: a 12 ft × 10 ft rectangle (120 ft²), a triangle with a 6 ft base and 4 ft height (12 ft²) and a circle 4 ft across (12.57 ft²) total 144.57 ft², which is 16.06 yd².
Method
How this calculator works
The shapes are plain geometry. The unit factors are exact definitions, so the only rounding is in what you see on screen.
Rectangle and triangle
Measure the sides in the same unit before you multiply. For a triangle, the height is measured straight up from the base, not along the slanted side.
Rectangle: Area = Length × WidthTriangle: Area = ½ × Base × HeightCircle
Enter the diameter, the distance straight across. The calculator halves it to get the radius. It uses the full value of π, not 3.14.
Circle: Area = π × (Diameter ÷ 2)²Several areas, one total
Each row is one area, and the calculator adds them. Doors, windows and cutouts are not subtracted, so measure around them or work them out separately and subtract by hand. Feet and inches become decimal feet first: 12 ft 6 in is 12.5 ft.
Total = Area 1 + Area 2 + Area 3 + ...Other units
These are exact definitions in NIST Handbook 44: 1 yd² = 9 ft², 1 acre = 43,560 ft², and 1 ft² = 0.09290304 m².
yd² = ft² ÷ 9m² = ft² × 0.09290304Acres = ft² ÷ 43,560Worked example: a rectangle, a triangle and a circle
Arithmetic checked| Step | Math | Result |
|---|---|---|
| Area 1: rectangle 12 ft × 10 ft | 12 × 10 | 120 ft² |
| Area 2: triangle, base 6 ft, height 4 ft | ½ × 6 × 4 | 12 ft² |
| Area 3: circle, 4 ft across | π × (4 ÷ 2)² | 12.566 ft² |
| Add the areas together | 120 + 12 + 12.566 | 144.566 ft² |
| Square yards | 144.566 ÷ 9 | 16.063 yd² |
| Square meters | 144.566 × 0.09290304 | 13.431 m² |
| Acres | 144.566 ÷ 43,560 | 0.0033 acre |
| Total area | about 144.57 ft² | |
With feet and inches: a room 12 ft 6 in by 10 ft 3 in is 12.5 × 10.25 = 128.125 ft², or 14.236 yd².
Disclaimer
Results are planning estimates based on the dimensions and assumptions you enter. They are not engineering, structural or building-code advice. Product yields, densities and coverage vary by manufacturer, batch and site conditions. Check product labels, your supplier and your local building department before you order materials or start work. Read the full calculation disclaimer.
Accuracy
What affects your estimate
The math cannot be wrong, but the answer is only as good as the measurements and the choice of what to count.
Where you measure
Measure the floor you will cover, wall to wall. An L-shaped room is two rectangles; add a row for each. A bay window or alcove is another row.
Openings and closets
This calculator adds areas and does not subtract. For paint or drywall, take the wall area and subtract openings yourself, or measure around them. The paint calculator does both steps from the room size, and the guide on how many square feet a gallon of paint covers turns wall area into gallons by hand.
Waste is a separate step
Square footage is the net area. Flooring, tile and paint need an allowance on top, and the right amount comes from the product and the layout. Add it where you order.
Square feet are flat
A pitched roof is larger than the floor plan under it, and a deep bed has volume as well as area. For those, use the roofing calculator or the cubic yard calculator.
Use these areas to plan and price materials. They are not a survey, and they do not replace a professional appraisal or survey of a home or lot.
Common mistakes
Measuring the slanted side of a triangle
The height is the straight-up distance from the base. The slanted edge is longer, and using it overstates the area.
Entering the radius as the diameter
The circle field wants the distance across. Typing the radius makes the area four times too small.
Mixing inches and feet
Multiplying 120 in by 10 ft gives a meaningless number. Use the feet and inches boxes, or type 12 ft 6 in, and let the calculator convert. For a length with no width, such as baseboard, use the linear feet calculator or read the guide on how to calculate linear feet.
Questions people ask
How do I calculate square feet?
For a rectangle, multiply length by width in feet. A 12 ft × 12 ft room is 144 ft². For other shapes, split them into rectangles, triangles and circles, find each area and add them. To see how your total compares, the guide on the average square footage of a house gives the U.S. Census figures.
How many square feet is a 30×40 area?
30 × 40 = 1,200 ft², which is 133.3 yd².
How do I get square yards from square feet?
Divide by 9. For example, 144 ft² ÷ 9 = 16 yd². The calculator shows square yards under the total, which is handy for carpet. The guide on square feet to square yards has a conversion table and carpet examples.
How many square feet are in an acre?
An acre is exactly 43,560 ft². The calculator shows acres for large areas, and the guide on square feet in an acre explains the conversion.
Can I type feet and inches?
Yes. Length fields accept entries like 12′ 6″ or 12 ft 6 in, and a plain number is read in the unit shown next to the field.
Related calculators and guides
Sources
Where the numbers come from
- NIST Handbook 44, Appendix C (square yard, acre and meter conversions), accessed October 16, 2026.