Enter length and width to find a rectangle area, perimeter, and diagonal.

Area, perimeter, and diagonal

A rectangle is described by its length and width, and from those two numbers everything else follows. Area, the space inside, is length times width. Perimeter, the distance around, is twice their sum. The diagonal comes straight from the Pythagorean theorem.

These are among the most used calculations in daily life, from flooring and paint to fabric and screens. A square is simply the special case where length and width are equal.

The formula

Worked example

A 10 by 6 rectangle has an area of 60, a perimeter of 32, and a diagonal of about 11.66.

How to read your result

Area is the space inside, perimeter is the distance around, and the diagonal follows from the Pythagorean theorem. A square is the special case where length equals width.

Frequently asked questions

How do I find the diagonal?

Use the Pythagorean theorem on the length and width.

What units does area use?

The square of whatever unit you enter.

Does this work for a square?

Yes, just enter equal length and width.

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