Area formulas
| Shape | Area |
|---|---|
| Rectangle | Length × Width |
| Square | Side² |
| Triangle | Base × Height ÷ 2 |
| Circle | π × r² |
| Trapezoid | (a + b) ÷ 2 × h |
| Parallelogram | Base × Height |
| Ellipse | π × a × b |
| Circle sector | π × r² × θ ÷ 360 |
Example: a circle with a 5 ft radius has an area of π × 5² = 78.54 sq ft (7.3 m²). A triangle with a 10 ft base and 6 ft height is 30 sq ft.
Tips
- Height for triangles and parallelograms is the straight, perpendicular height, not the slanted side.
- For a circle measured across, the radius is half the diameter.
- Irregular rooms and yards: split into rectangles and triangles, then add. The square footage calculator does this for rooms.
Need volume instead? Use the cubic yard calculator.
Frequently asked questions
How do you find the area of a circle?
Multiply π (about 3.1416) by the radius squared. A circle 10 ft across has a radius of 5 ft and an area of 78.54 sq ft.
How do you find the area of a triangle?
Multiply the base by the perpendicular height and divide by 2.
How many square feet in an acre?
43,560 square feet, about 4,047 square meters.
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