How do I calculate rectangle area?

Rectangle area is calculated by multiplying length by width: Area = Length × Width. For example, a rectangle with length 10 and width 5 has an area of 50 square units.

What is the difference between a rectangle and a square?

A square is a special type of rectangle where all four sides are equal. Both use the same area formula (length × width), but in a square, length equals width.

How do I find the perimeter of a rectangle?

The perimeter is calculated by adding all four sides: Perimeter = 2 × (Length + Width). This formula works because opposite sides are equal in a rectangle.

How do I calculate the diagonal of a rectangle?

The diagonal can be found using the Pythagorean theorem: Diagonal = √(Length² + Width²). This creates a right triangle with the diagonal as the hypotenuse.

What units should I use?

You can use any units (meters, feet, inches, etc.) as long as all measurements use the same unit. Area will be in square units, and perimeter/diagonal will be in the same unit as the sides.

Can I use this for squares?

Yes, this calculator works perfectly for squares. Just enter the same value for both length and width. The formulas remain the same, but all sides will be equal.

Rectangle Area Calculator

Find area, perimeter, and diagonal of rectangles and squares. Enter length and width to get comprehensive geometric measurements instantly.

Calculator

Result

Area: -
Perimeter: -
Diagonal: -

Formula & Guide

Formulas

A

Area

Area = Length × Width

Multiply length by width

P

Perimeter

Perimeter = 2 × (Length + Width)

Add length and width, then multiply by 2

D

Diagonal

Diagonal = √(Length² + Width²)

Pythagorean theorem

Formula Variables

Length

The longer side (or any side) of the rectangle

Width

The shorter side (or adjacent side) of the rectangle

Area

The amount of space inside the rectangle, measured in square units

Perimeter

The total distance around the rectangle

Step-by-Step Scenario

Example Scenario

Length

10 units

Width

5 units

1

Calculate Area

Area = Length × Width
Area = 10 × 5

Area = 50 square units

2

Calculate Perimeter

Perimeter = 2 × (Length + Width)
Perimeter = 2 × (10 + 5)
Perimeter = 2 × 15

Perimeter = 30 units

3

Calculate Diagonal

Diagonal = √(Length² + Width²)
Diagonal = √(10² + 5²)
Diagonal = √(100 + 25) = √125

Diagonal ≈ 11.18 units

Additional Examples

Square

Length: 6 units

Width: 6 units

Area

6 × 6 = 36 square units

Perimeter

2 × (6 + 6) = 24 units

Large Rectangle

Length: 15 units

Width: 8 units

Area

15 × 8 = 120 square units

Perimeter

2 × (15 + 8) = 46 units

Characteristics of Rectangles

Simple Formula

Rectangle area uses the simplest geometric formula: just multiply length by width. This makes it easy to calculate and understand.

Square as Special Case

A square is a rectangle with equal sides. When length equals width, you have a square, and the formulas still apply.

Practical Applications

Used extensively in construction, architecture, flooring, painting, landscaping, and any field involving rectangular spaces.

Right Angles

All rectangles have four right angles (90 degrees), making them perfect for construction and design applications.

Important Notes

Length and width can be interchanged - the area remains the same regardless of which dimension is called length or width.
For squares, enter the same value for both length and width. The formulas work the same way.
Area is always expressed in square units (e.g., square meters, square feet) based on the units of the input measurements.
The diagonal divides the rectangle into two congruent right triangles, which is why the Pythagorean theorem applies.
Perimeter represents the total distance around the rectangle, useful for fencing, framing, and border calculations.

Frequently Asked Questions

Find answers to common questions about rectangle calculations.