Rhombus Perimeter Calculator
A rhombus is a quadrilateral with four equal sides, so its perimeter is four times the side length. You can also find the perimeter from the two diagonals: because they cross at right angles and bisect each other, each side is the hypotenuse of a right triangle with legs equal to half of each diagonal. Enter either the side or both diagonals. The calculator returns the perimeter, the side, and the area when diagonals are given. All formulas are exact geometric results.
Rhombus formulas
Side from diagonals = square root of ((d1/2) squared + (d2/2) squared)
Perimeter = 4 x side
Area = (d1 x d2) / 2
Half-perimeter = 2 x side
If you enter a side, the perimeter is 4 times it. If you enter both diagonals, the side comes from the Pythagorean theorem and takes precedence; the area is then half the product of the diagonals.
Rhombus geometry context
- All four sides of a rhombus are equal in length.
- The diagonals cross at right angles and bisect each other.
- A square is a rhombus with equal diagonals and right angles.
- Area equals half the product of the diagonals, regardless of angle.
- Use one length unit; area is reported in that unit squared.
Rhombus perimeter: frequently asked questions
How do you find the perimeter of a rhombus?
A rhombus has four equal sides, so its perimeter is four times the side length: P = 4s. If you instead know the two diagonals, the side equals half the square root of the sum of the squared diagonals, because the diagonals of a rhombus bisect each other at right angles. The perimeter is then four times that side.
How are the side and diagonals related?
The diagonals of a rhombus cross at right angles and cut each other in half. Each side is the hypotenuse of a right triangle with legs equal to half of each diagonal. So side = square root of ((d1/2) squared + (d2/2) squared). This is a direct use of the Pythagorean theorem.
What is the area of a rhombus?
The area of a rhombus is half the product of its diagonals: A = (d1 x d2) / 2. This calculator computes the area when you enter the diagonals. The diagonal method is exact and convenient because the diagonals are often the easiest measurements to take.
Is a square a rhombus?
Yes. A square is a special rhombus in which all four angles are also right angles and the two diagonals are equal. Every formula here applies to a square as a particular case, with equal diagonals giving equal sides and a perimeter of four times the side.
Which inputs should I use?
Use the side length if you know it directly for the perimeter. Use both diagonals if those are what you measured; the calculator then derives the side and the area. Enter only the side if you do not have the diagonals, in which case the area is left as not available because it cannot be found from the side alone.
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.