Rectangle Calculator — Area, Perimeter, Diagonal & Properties
Calculate the area, perimeter, and diagonal of any rectangle instantly. Enter length and width to get all properties with clear formulas and step-by-step solutions. Ideal for geometry homework, construction planning, and real-world measurements.
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A rectangle is a special parallelogram where all four angles are exactly 90° A square is a special rectangle where length equals width The diagonal divides a rectangle into two congruent right triangles A rectangle's area is maximized (for a given perimeter) when it's a square — the isoperimetric property The golden rectangle (ratio ≈ 1.618:1) is considered the most aesthetically pleasing proportion
Ready to run the numbers?
Why: Rectangles are the most common shape in the built environment — rooms, screens, books, fields, and construction materials are all rectangular. Calculating their area is essential for flooring, painting, and land measurement. Perimeter matters for fencing and framing. The diagonal — derived from the Pythagorean theorem — is critical for checking squareness in construction (the '3-4-5 rule').
How: Enter the length and width of your rectangle. The calculator instantly computes the area (l × w), perimeter (2l + 2w), and diagonal (√(l² + w²)). All results update in real time as you type. The diagonal formula is a direct application of the Pythagorean theorem applied to the right triangle formed by the length, width, and diagonal.
Run the calculator when you are ready.
Area
Perimeter
Diagonal
Rectangle Properties
Area Calculation
The area of a rectangle is the amount of space it occupies in two dimensions.
Perimeter Calculation
The perimeter of a rectangle is the total distance around its edges.
Diagonal Calculation
The diagonal of a rectangle is the straight line connecting opposite corners.
Special Cases
Square
A rectangle with equal length and width is a square. For a square with side length s:
Area = s²
Perimeter = 4s
Diagonal = s√2
Golden Rectangle
A rectangle where the ratio of length to width is the golden ratio (approximately 1.618:1). These rectangles are considered to be aesthetically pleasing and appear in art, architecture, and nature.
For educational and informational purposes only. Verify with a qualified professional.
🧮 Fascinating Math Facts
Most modern smartphones have screen aspect ratios between 19.5:9 and 20:9 — much more elongated than the classic 16:9 TV ratio.
— GSMArena
A FIFA soccer field is 100–110m × 64–75m, giving an area of 6,400–8,250 m². The penalty area is itself a precisely defined rectangle.
— FIFA Laws of the Game
A4 paper (210 × 297 mm) uses the √2 ratio — so folding it in half gives another rectangle with the same proportions.
— ISO 216
The golden rectangle (≈1.618:1 ratio) appears in ancient Greek architecture, Renaissance art, and the spiral shells of nautilus mollusks.
— Wolfram MathWorld
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