Rectangle Calculator
Calculate rectangle area, perimeter, diagonal, and aspect ratio from length and width with complete mathematical steps.
Did this calculation save you time?
Student ProjectHi! I'm a student developer building Calculat in my spare time. I was tired of searching for basic math tools and having to click through 10 spammy popups, loan ads, and cookie trackers.
I keep this website 100% free, private, and ad-free. If this helped you with your homework, project, or finances today, bookmarking this page or telling a friend helps me keep building more free tools!
What Is a Rectangle Calculator?
A rectangle is a four-sided quadrilateral with four right angles (90°). Opposite sides are parallel and equal in length, and both diagonals are equal in length and bisect each other.
How to Use This Calculator
- Enter the length (l) and width (w) of the rectangle.
- View the calculated Area, Perimeter, Diagonal, and simplified Aspect Ratio.
- Review the step-by-step mathematical calculations.
Rectangle Dimensions Formulas
A = l \times w, \quad P = 2(l + w), \quad d = \sqrt{l^2 + w^2}Area is the product of length and width. Perimeter is twice the sum of length and width. Diagonal is found via the Pythagorean theorem.
Worked Example
Scenario: Calculate a rectangle with length l = 10 m and width w = 6 m
Area: A = 10 × 6 = 60 m²
Perimeter: P = 2 × (10 + 6) = 2 × 16 = 32 m
Diagonal: d = √(10² + 6²) = √(100 + 36) = √136 ≈ 11.6619 m
Aspect Ratio: 10:6 reduces to 5:3
Tips & Key Notes
- If length equals width, the rectangle is a square.
- The diagonal splits the rectangle into two congruent right-angled triangles.
- To find length given area and width, divide area by width: l = A / w.
Frequently Asked Questions
How do you calculate the diagonal of a rectangle?
Apply the Pythagorean theorem: d = √(length² + width²).
Is a square considered a rectangle?
Yes, a square is an equiangular quadrilateral with four 90° angles, making it a special equilateral rectangle.
What is aspect ratio?
Aspect ratio is the proportional relationship between width and height, expressed as two integers separated by a colon (e.g. 16:9, 4:3).
How do you find the perimeter of a rectangle?
Add length and width together, then multiply by 2: P = 2(l + w).
Related Calculators
Explore similar toolsSquare Calculator
Calculate square area, perimeter, diagonal, inradius, and circumradius from side length with step-by-step formulas.
Cuboid Calculator
Calculate cuboid (rectangular prism) volume, total surface area, lateral area, and space diagonal from length, width, and height.
Parallelogram Calculator
Calculate parallelogram area, perimeter, base, height, and side lengths with step-by-step geometric formulas.