Rectangle Calculator
Calculate area, perimeter, diagonal, and side lengths of any rectangle. Enter any two values and instantly solve for all the rest.
| Property | Value |
|---|
Rectangle Formulas Reference
Rectangle formulas are the foundation for all rectangle calculations. All four properties are related through three core equations.
Area: A = a × b
Perimeter: P = 2a + 2b
Diagonal: d = √(a² + b²)
where a and b are the two side lengths.
| Known Values | Formula for Unknown |
|---|---|
| a and b | A = ab, P = 2a+2b, d = √(a²+b²) |
| Area A and side a | b = A/a |
| Area A and side b | a = A/b |
| Perimeter P and side a | b = (P − 2a) / 2 |
| Perimeter P and side b | a = (P − 2b) / 2 |
| Diagonal d and side a | b = √(d² − a²) |
| Diagonal d and side b | a = √(d² − b²) |
Rectangle Properties Explained
Rectangle properties are defined by four key measurements that are all mathematically linked through the formulas above.
Area of a Rectangle
The area of a rectangle measures the two-dimensional space inside its boundaries, expressed in square units. It is calculated by multiplying side a (length) by side b (width). Doubling either side doubles the area. If you know the area and one side, simply divide to find the other.
Perimeter of a Rectangle
The perimeter is the total distance around the outside of the rectangle. Since opposite sides of a rectangle are equal, the perimeter equals two times the sum of both sides: P = 2(a + b). Perimeter is always measured in the same linear units as the sides.
Diagonal of a Rectangle
A rectangle has two diagonals, both equal in length. The diagonal connects opposite corners and is calculated using the Pythagorean theorem because the diagonal, the length, and the width form a right triangle. The formula is d = √(a² + b²). The diagonal is always longer than either side individually.