Parallelogram Perimeter Calculator
A parallelogram has two pairs of equal, parallel opposite sides, so its perimeter is twice the sum of two adjacent sides. Enter the two side lengths and this calculator returns the perimeter; add the base and perpendicular height and it also returns the area. Remember that the area uses the perpendicular height between the parallel sides, not the slanted side length, which is the most common mistake. Rectangles, squares and rhombi are all special parallelograms covered by these exact formulas.
Parallelogram formulas
Perimeter = 2 x (side a + side b)
Area = base x perpendicular height
Sum of adjacent sides = side a + side b
Semi-perimeter = side a + side b
The perimeter uses the two distinct side lengths because opposite sides are equal. The area uses the perpendicular height, the distance between the parallel sides, not the slanted side.
Parallelogram geometry context
- Opposite sides of a parallelogram are equal and parallel.
- Opposite angles are equal and adjacent angles add to 180 degrees.
- A rectangle, square and rhombus are all special parallelograms.
- Area uses the perpendicular height, never the slanted side length.
- Use one length unit; area is reported in that unit squared.
Parallelogram perimeter: frequently asked questions
How do you find the perimeter of a parallelogram?
A parallelogram has two pairs of equal opposite sides, so its perimeter is twice the sum of two adjacent sides: P = 2 x (a + b). For sides of 8 and 5 units the perimeter is 2 x (8 + 5) = 26 units. This calculator also returns the area when you enter the base and height.
What is the area of a parallelogram?
The area is the base multiplied by the perpendicular height: A = base x height. The height is the perpendicular distance between the base and its opposite side, not the slanted side length. Using the slant side instead of the perpendicular height is the most common error.
Why is the slant side not used for area?
Area measures the space enclosed, which depends on how far apart the two parallel sides are, that is, the perpendicular height. The slanted side is longer than this height whenever the parallelogram leans, so using it would overstate the area. Always use the perpendicular height.
Is a rectangle a parallelogram?
Yes. A rectangle is a parallelogram with right angles, so its perimeter is also 2 x (a + b) and its area is base times height, where the height equals the adjacent side because the angle is 90 degrees. Squares and rhombi are also special parallelograms.
What units should I use?
Use the same length unit for both sides and for the height. The perimeter is then in that length unit and the area is in that unit squared. If your height is in different units from the sides, convert first so the area is correct.
Official sources
- U.S. National Institute of Standards and Technology: Digital Library of Mathematical Functions.
- NASA: Geometry and area reference.
Reviewed by the CalculatorHub team, edited by James Graham, 16 June 2026. See our methodology.