What formulas does this calculator use?

Area = length × width; Perimeter = 2(length + width); Diagonal = √(length² + width²).

How is a rectangle different from a square?

A square is a special rectangle where all four sides are equal.

What real-world objects are rectangle-shaped?

Doors, windows, books, and screens are common examples.

Rectangle Calculator - Area, Perimeter & Diagonal

Rectangle Calculator

Calculate the area, perimeter, and diagonal of any rectangle or square in a few seconds.

Length

Width

Units

Area-

Perimeter-

Diagonal-

What Is a Rectangle Calculator?

This calculator finds the area, perimeter, and diagonal length of a rectangle (or square, when length equals width) from its length and width.

Rectangle Formulas

Area: A = length × width
Perimeter: P = 2 × (length + width)
Diagonal: d = √(length² + width²)

How to Use This Calculator

Enter the rectangle's length and width in the same unit.
Select the unit of measurement.
Click Calculate to get the area, perimeter, and diagonal instantly.

Worked Example

A rectangular room measures 12 ft by 8 ft. The area is 12 × 8 = 96 ft². The perimeter is 2 × (12 + 8) = 40 ft. The diagonal is √(12² + 8²) = √208 ≈ 14.42 ft. Try entering 12 and 8 above to check.

Common Uses

Useful for flooring and paint estimates, fencing a yard, sizing a rug, framing a picture, or any layout that needs area, perimeter, or diagonal measurements.