How do you find the diagonal of a rectangle?

The diagonal equals √(width² + height²) by the Pythagorean theorem, since the diagonal forms the hypotenuse of a right triangle.

What is the diagonal angle?

It is the angle the diagonal makes with the base (width), calculated as arctan(height ÷ width) in degrees.

Does this tool upload my measurements?

No — every calculation runs locally in your browser and nothing is sent anywhere.

Rectangle Calculator

Area, perimeter and diagonal of a rectangle.

Rectangle calculator

Enter the width and height of a rectangle and this tool returns its area, perimeter, diagonal length and the angle the diagonal makes with the base.

Area is width × height, perimeter is 2 × (width + height), and the diagonal is √(width² + height²). All maths runs in your browser — nothing is uploaded.