Quadrilateral Calculator — Area & Perimeter
Select a quadrilateral type (rectangle, parallelogram, trapezoid or rhombus), enter its dimensions, and instantly get area, perimeter, and the diagonal or side length.
Shape
- 1
Length × width
8 × 5 = 40
How does this calculator work?
Rectangle: A = a·b, diagonal = √(a²+b²). Parallelogram: A = base×height. Isosceles trapezoid: A = (a+b)h/2, leg = √(h²+((a−b)/2)²). Rhombus: A = d₁·d₂/2, side = √((d₁/2)²+(d₂/2)²), P = 4·side. Select the shape and enter the relevant dimensions to get area, perimeter, and key measurements instantly.
Formula
How this is calculated
A quadrilateral is any closed polygon with four straight sides. Different special cases have clean formulas. For a rectangle, area = length × width, perimeter = 2(a + b), and the diagonal follows the Pythagorean theorem: d = √(a² + b²). A parallelogram has the same perimeter formula 2(a + b), but the area = base × perpendicular height (not the slant side). The height is the distance between the two parallel sides measured at a right angle — always shorter than the slant side for an oblique parallelogram.
For a trapezoid the two parallel sides are called the bases (a and b). The area equals the average of the bases times the height: A = (a + b)/2 × h. This calculator assumes an isosceles trapezoid — the two non-parallel legs are equal — so the leg length follows from the right triangle formed by the height, half the base difference, and the leg: leg = √(h² + ((a − b)/2)²). A rhombus has all four sides equal and its diagonals bisect each other at right angles. Enter the two diagonals d₁ and d₂: area = d₁ × d₂/2, and the side length = √((d₁/2)² + (d₂/2)²) by Pythagoras.
All formulas assume exact inputs. For real measured values, rounding in the measurements propagates into the results — treat them as estimates. Angle information is not needed for any of the quantities calculated here.
Frequently asked questions
A rectangle is a special parallelogram with all right angles. Both share the perimeter formula 2(a+b), but for a rectangle the perpendicular height equals the shorter side b, so the area simplifies to a×b. An oblique parallelogram needs the perpendicular height separately because the slant side is longer than the height.
An isosceles trapezoid has two equal legs, which lets the leg length be derived from the bases and height alone. For a general (scalene) trapezoid with unequal legs you need to enter each leg directly — those calculators handle specific configurations.
The diagonals of a rhombus bisect each other at right angles and are easy to measure directly. All other properties (side, area, perimeter) follow from them via the Pythagorean theorem. Alternatively, if you know the side and one angle you can find the diagonals first.
Also known as
TG we-Calculate Editorial Team. (2026). Quadrilateral Calculator — Area & Perimeter [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/quadrilateral-calculator
TG we-Calculate Editorial Team. "Quadrilateral Calculator — Area & Perimeter." TG we-Calculate. 2026. https://we-calculate.com/calculator/quadrilateral-calculator.
TG we-Calculate Editorial Team, "Quadrilateral Calculator — Area & Perimeter," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/quadrilateral-calculator
@misc{wecalculate_quadrilateral_calculator, title = {Quadrilateral Calculator — Area & Perimeter}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/quadrilateral-calculator}}, year = {2026}, note = {TG we-Calculate} }
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