Geometry Calculator
Calculate area and perimeter for circles, rectangles, squares, triangles, trapezoids, and parallelograms.
A = π × r² | C = 2π × r
Reference Examples
| Shape | Example | Area | Perimeter |
|---|---|---|---|
| Circle | r = 10 cm | 314.16 | 62.83 |
| Rectangle | 21 × 29.7 cm | 623.7 | 101.4 |
| Square | 30 × 30 cm | 900 | 120 |
| Triangle | b=10, h=6 cm | 30 | — |
| Trapezoid | a=8, b=12, h=5 cm | 50 | — |
| Parallelogram | b=10, h=4 cm | 40 | — |
Frequently Asked Questions
The area of a circle is A = π × r², where r is the radius. For a circle with radius 10 cm, the area = π × 100 ≈ 314.16 cm². The circumference (perimeter) is C = 2π × r ≈ 62.83 cm.
The area of a triangle is A = ½ × base × height. For example, a triangle with base 10 cm and height 6 cm has area = ½ × 10 × 6 = 30 cm². Note: height must be perpendicular to the base, not the slant side.
The area of a trapezoid is A = ½ × (a + b) × h, where a and b are the two parallel sides and h is the perpendicular height between them. For a trapezoid with parallel sides 8 cm and 12 cm, and height 5 cm: A = ½ × (8 + 12) × 5 = 50 cm².
Area is the amount of space inside a 2D shape, measured in square units (cm², m², etc.). Perimeter is the total length of the boundary (all sides added together), measured in regular units (cm, m, etc.). For a rectangle 10 cm × 5 cm: area = 50 cm², perimeter = 30 cm.