# Area of Rectangle Calculator

Calculate the area, perimeter, and diagonal of a rectangle from length and width. Free online rectangle calculator with instant results and formulas.

## What this calculates

Calculate the area, perimeter, and diagonal of any rectangle by entering its length and width. This fundamental geometry calculator provides instant results for one of the most common shapes in construction, design, and everyday math.

## Inputs

- **Length** — min 0 — The length (longer side) of the rectangle.
- **Width** — min 0 — The width (shorter side) of the rectangle.

## Outputs

- **Area** — The area of the rectangle (length x width).
- **Perimeter** — The perimeter of the rectangle (2 x (length + width)).
- **Diagonal Length** — The length of the diagonal (sqrt(length^2 + width^2)).

## Details

A rectangle is a four-sided polygon with four right angles (90 degrees). Opposite sides are equal in length and parallel. The key formulas for a rectangle are:

Rectangle Formulas

- Area: A = length x width

- Perimeter: P = 2 x (length + width)

- Diagonal: d = sqrt(length^2 + width^2)

The diagonal formula comes from the Pythagorean theorem, since the diagonal divides the rectangle into two right triangles. A square is a special case of a rectangle where the length equals the width.

Rectangle calculations are essential in real estate (room areas, lot sizes), construction (flooring, painting, fencing), interior design (furniture placement), agriculture (field areas), and manufacturing (material cutting). Understanding these formulas helps with cost estimation, material planning, and spatial optimization.

## Frequently Asked Questions

**Q: How do I calculate the area of a rectangle?**

A: Multiply the length by the width: Area = length x width. For example, a rectangle that is 8 meters long and 5 meters wide has an area of 8 x 5 = 40 square meters. Make sure both measurements use the same units.

**Q: How do I find the diagonal of a rectangle?**

A: Use the Pythagorean theorem: diagonal = sqrt(length^2 + width^2). For a rectangle with length 6 and width 8, the diagonal = sqrt(36 + 64) = sqrt(100) = 10. The diagonal divides the rectangle into two congruent right triangles.

**Q: What is the difference between a rectangle and a square?**

A: A square is a special rectangle where all four sides are equal. Every square is a rectangle, but not every rectangle is a square. A rectangle has two pairs of equal sides (length and width), while a square has all four sides equal.

**Q: How much fencing do I need for a rectangular yard?**

A: You need the perimeter: P = 2 x (length + width). For a yard that is 30 feet by 20 feet, the perimeter is 2 x (30 + 20) = 100 feet of fencing. If there is an opening (like a gate), subtract that width from the total.

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Source: https://vastcalc.com/calculators/math/area-of-rectangle
Category: Math
Last updated: 2026-04-21