Rectangle and trapezoid
A 4 × 3 rectangle: area 12, perimeter 14. A trapezoid with parallel sides 4 and 8, height 3 and slanted sides of 5: area 18, perimeter 22.
Area and Perimeter Calculator
Area and perimeter of squares, rectangles, triangles, trapezoids, ellipses, polygons and more.
Result
Enter every measurement, in the same unit.
Runs in your browser — nothing you enter is sent to a server.
How the Area and Perimeter Calculator works
Choose a shape and enter its measurements in one unit; the area comes out in that unit squared and the perimeter in the unit. Triangles use three sides (Heron's formula). The ellipse perimeter has no exact formula, so Ramanujan's very accurate approximation is used.
Formulas
Common shapes
rectangle l × w; triangle √(s(s−a)(s−b)(s−c)); trapezoid (a + b) ÷ 2 × h; rhombus d₁ × d₂ ÷ 2
Regular polygon
area = n × s² ÷ (4 tan(π ÷ n))
Ellipse perimeter (Ramanujan)
π[3(a + b) − √((3a + b)(a + 3b))]
Examples
Hexagon and ellipse
A regular hexagon with 2-unit sides has an area of about 10.3923. An ellipse with semi-axes 10 and 5 has a perimeter of about 48.4421.
Frequently asked questions
Why does a parallelogram need a height?
Its area is base × height, where the height is the straight distance between the bases, not the slanted side.
How accurate is the ellipse perimeter?
Ramanujan's formula is exact for circles and within a tiny fraction of a percent for everyday ellipses.
Can I use different units?
Enter every measurement in the same unit, and convert results with the Area Converter.
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