Formulas used
Square: area = side², perimeter = 4 × side. Rectangle: area = base × height, perimeter = 2 × (base + height). Triangle (from the 3 sides, Heron's formula): semi-perimeter s = (a+b+c)/2, area = √(s(s-a)(s-b)(s-c)), perimeter = a+b+c. Circle: area = π × radius², perimeter (circumference) = 2 × π × radius. Isosceles trapezoid: area = ((longer base + shorter base) / 2) × height, perimeter = longer base + shorter base + 2 × leg. Parallelogram: area = base × height, perimeter = 2 × (base + side). Rhombus: area = (longer diagonal × shorter diagonal) / 2, perimeter = 4 × side (the side is derived from the diagonals via the Pythagorean theorem).
Area unit
If measurements are entered in meters, area comes out in square meters (m²) and perimeter in meters (m) — the calculator doesn't convert units, so always use the same unit across all fields of a shape.
Frequently asked questions
Why does the triangle ask for 3 sides instead of base and height?
Because with the 3 sides (Heron's formula) you can calculate the area of any triangle without needing to measure the height, which is usually harder to get in practice than measuring the sides.
Does it work for a trapezoid with different (non-isosceles) legs?
The area works for any trapezoid, since it only depends on the bases and the height. The perimeter, however, assumes both non-parallel sides are equal (isosceles trapezoid) — for an irregular trapezoid, manually add up the 4 real sides.