Rectangle Calculator
Calculate rectangle area, perimeter, diagonal, and aspect ratio. Enter two sides and get all measurements instantly with interactive visualization.
A = a x b | P = 2(a + b) | d = sqrt(a² + b²)Rectangle Properties
Area
40.0000 cm²
Rectangle Dimensions
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Common rectangle sizes
Rectangle Visualization
Complete Results
Side a
8.0000 cm
Side b
5.0000 cm
Area
40.0000 cm²
A = a x b
Perimeter
26.0000 cm
P = 2(a + b)
Diagonal
9.4340 cm
d = sqrt(a² + b²)
Aspect Ratio
0:0
(1.6000:1)
Inscribed Circle Radius
2.5000 cm
r = min(a,b) / 2
Circumscribed Circle Radius
4.7170 cm
R = d / 2
Common Rectangle Sizes
| Name | Dimensions | Aspect Ratio | Use Case |
|---|---|---|---|
| A4 Paper | 210 x 297 mm | 1:1.414 | Documents |
| US Letter | 8.5 x 11 in | 1:1.294 | Documents |
| HD Video | 1920 x 1080 px | 16:9 | Video/TV |
| 4K Video | 3840 x 2160 px | 16:9 | Video/TV |
| Instagram Post | 1080 x 1080 px | 1:1 | Social Media |
| Golden Rectangle | 1 x 1.618 | 1:1.618 | Art/Design |
| Credit Card | 85.6 x 53.98 mm | 1.586:1 | Finance |
Rectangle Formulas
Basic Formulas
- Area: A = a x b
- Perimeter: P = 2a + 2b = 2(a + b)
- Diagonal: d = sqrt(a² + b²)
Derived Values
- a from A & b: a = A / b
- a from P & b: a = (P / 2) - b
- Aspect Ratio: a / b
Note: A rectangle has four right angles (90 degrees), making it a special case of a parallelogram. The diagonals bisect each other and are equal in length.
Rectangle Properties
Area
40.0000 cm²
?How to Calculate Rectangle Properties
Rectangle formulas: Area = length x width. Perimeter = 2(length + width). Diagonal = square root of (length squared + width squared). The aspect ratio is expressed as length:width. All measurements can be calculated from any two known values.
What is a Rectangle?
A rectangle is a quadrilateral with four right angles. Opposite sides are equal and parallel. Key measurements include length (longer side), width (shorter side), area (space enclosed), perimeter (total boundary length), and diagonal (line connecting opposite corners). The diagonals of a rectangle bisect each other and are equal in length.
Key Facts About Rectangles
- Area = length x width (A = a x b)
- Perimeter = 2(length + width) = 2a + 2b
- Diagonal = sqrt(a^2 + b^2) using Pythagorean theorem
- A rectangle has 4 right angles (90 degrees each)
- Opposite sides are equal and parallel
- The diagonals of a rectangle are equal in length
- Aspect ratio is the ratio of length to width (a:b)
- A square is a special rectangle where a = b
Practice Rectangle Problems
Test your understanding of rectangles
Practice with 4 problems to test your understanding.
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Quick Answer
Rectangle formulas: Area = length x width. Perimeter = 2(length + width). Diagonal = square root of (length squared + width squared). The aspect ratio is expressed as length:width. All measurements can be calculated from any two known values.
Frequently Asked Questions
The area (A) of a rectangle is calculated by multiplying the length by the width: A = length x width, or A = a x b. This gives you the total space enclosed by the rectangle in square units.
The perimeter (P) is the total distance around the rectangle. P = 2(length + width) = 2(a + b) = 2a + 2b. You add all four sides together, or simply double the sum of length and width.
The diagonal (d) connects opposite corners of the rectangle. Using the Pythagorean theorem: d = sqrt(a^2 + b^2), where a and b are the sides. Both diagonals of a rectangle are equal in length.
Aspect ratio describes the proportional relationship between width and height of a rectangle, expressed as a:b or as a decimal. Common aspect ratios include 16:9 (widescreen), 4:3 (standard), and 1:1 (square).
A golden rectangle has an aspect ratio equal to the golden ratio (approximately 1.618:1). This ratio appears frequently in nature, art, and architecture and is considered aesthetically pleasing.
A square is a special type of rectangle where all four sides are equal (a = b). While every square is a rectangle, not every rectangle is a square. Squares have all the properties of rectangles plus equal sides.
Last updated: 2025-01-15
Rectangle Properties
Area
40.0000 cm²