Pick a shape and enter its measurements. You'll get the area with the formula and working, converted to square feet, square meters, square yards and acres.
Area formulas
| Shape | Formula | Example |
|---|
| Rectangle | length × width | 12 × 10 = 120 |
| Square | side² | 9² = 81 |
| Circle | π × radius² | π × 5² ≈ 78.54 |
| Triangle | ½ × base × height | ½ × 8 × 6 = 24 |
| Triangle from 3 sides | Heron's formula: √(s(s − a)(s − b)(s − c)), s = half the perimeter | 3, 4, 5 → 6 |
| Trapezoid | ½ × (side a + side b) × height | ½ × (6 + 10) × 4 = 32 |
| Parallelogram | base × height | 7 × 3 = 21 |
| Ellipse | π × a × b (the two half-widths) | π × 4 × 2 ≈ 25.13 |
| Sector | (angle ÷ 360) × π × radius² | 90° of radius 4 ≈ 12.57 |
Square feet, square meters and acres
Area units are the length unit squared, so converting them uses the length factor twice. 1 foot is 0.3048 meters, so 1 square foot is 0.3048² = 0.09290304 square meters, and 1 square meter is about 10.764 square feet. An acre is 43,560 square feet, and a hectare is 10,000 square meters (about 2.471 acres).
Rooms and odd shapes
For an L-shaped room, split it into two rectangles, find each area and add them. For flooring, tile or paint, the flooring and paint calculators add the extra you need for cuts and waste.
How we checked this
Before every update, this calculator is run in a real browser with these known answers, and it must match all of them:
- Rectangle 12 ft × 10 ft = 120 square feet = 11.148365 m² ✓
- Circle of radius 5 = 78.53981634 ✓
- Triangle with sides 3, 4, 5 = 6 (Heron) ✓
- Trapezoid ½ × (6 + 10) × 4 = 32 ✓
- Quarter circle of radius 4 = 12.56637061 ✓
- 43,560 sq ft (208.710326 ft square) is 1 acre ✓
Last checked October 26, 2026. Spotted something wrong? The math is done in your browser with the formula shown on this page, so you can check any result by hand.
Questions people ask
How do I calculate square feet?
Multiply the length by the width, both in feet. A room 12 feet by 10 feet is 120 square feet. If you measured in inches, divide the result by 144.
How do I find the area of a circle?
Multiply π (about 3.14159) by the radius squared. A circle 10 feet across has a radius of 5, so its area is π × 25 ≈ 78.54 square feet.
How many square feet are in an acre?
43,560 square feet. A square acre is about 208.7 feet on each side.
How do I find the area of a triangle without the height?
Use Heron's formula with the three side lengths. Choose 'Triangle (three sides)' above and Calcist does it for you.