Area of a Rectangle Calculator
Whether you need to know the area of a carpet, a parcel, a TV screen, a rectangle pool, or a window, this area of a rectangle calculator will solve your problem in a blink of an eye! All you have to do is input the length and width and allow this rectangle calc to find the values of P (perimeter), A (area), and D (diagonal).
🙋 Feeling confident? Try our quick quiz and see how well you really know rectangle calculations!
What is a rectangle?
A rectangle is a quadrilateral with four right angles. We may also define it in another way: a parallelogram containing a right angle — if one angle is right, the others must be the same. Moreover, each side of a rectangle has the same length as the one opposite to it. The adjacent sides need not be equal, in contrast to a square, which is a special case of a rectangle.
If you know some Latin, the name of a shape usually explains a lot. The word rectangle comes from the Latin rectangulus. It's a combination of rectus (which means "right, straight") and angulus (an angle), so it may serve as a simple, basic definition of a rectangle.
A rectangle is an example of a quadrilateral. You can use our quadrilateral calculator to find the area of other types of quadrilateral.
How to find the area of a rectangle?
The image above shows a typical rectangle. It has four sides and four right angles. The lengths of its sides are denoted with a and b, while the length of the diagonal is denoted with d.
If all sides of the rectangle have equal lengths, we call it a square.
The area of a rectangle is a space restricted by its sides or, in other words, within the perimeter of a rectangle. To find the area of a rectangle, all you need to do is a multiplication of rectangular sides a and b:
Area = a × bRectangle formulas
All rectangle formulas are presented below:
Rectangle calc: find A (area)
A = a × bRectangle calc: find P (perimeter)
P = 2 × (a + b)Rectangle calc: find D (diagonal)
d = √(a² + b²)The diagonal formula comes directly from the Pythagorean theorem — the diagonal is the hypotenuse of the right triangle formed by the two sides of the rectangle.
Golden rectangle
A golden rectangle is a rectangle whose side lengths are in the golden ratio, approximately 1 : 1.618 (or more precisely, 1 : φ where φ = (1 + √5) / 2 ≈ 1.6180339887…). The golden ratio has fascinated mathematicians, architects, and artists for centuries.
The Parthenon, many paintings by Leonardo da Vinci, and even the proportions of credit cards are said to approximate the golden rectangle. Our calculator automatically detects when your rectangle is close to golden proportions!
Properties of a rectangle
- All four angles are right angles (90°)
- Opposite sides are equal in length and parallel
- The diagonals bisect each other (cut each other in half)
- Both diagonals are equal in length
- A rectangle is a special case of a parallelogram
- A square is a special case of a rectangle (when a = b)
Rectangle vs. other shapes — Is a square a rectangle?
Yes! A square is a special type of rectangle where all four sides are equal. Every square is a rectangle, but not every rectangle is a square.
Similarly, every rectangle is a parallelogram (opposite sides parallel and equal), but not every parallelogram is a rectangle (it must also have right angles).
Weird fun fact: What's the most rectangular shaped country in the world?
Egypt is often cited as one of the most rectangular countries, with its borders forming a nearly perfect rectangle along the Nile delta. However, Vatican City and various small territories also have remarkably rectangular outlines. Geographers have actually quantified the "rectangularity" of countries — a fun application of rectangle geometry!
Rectangle patterns
Rectangles appear everywhere in nature and human design:
- Honeycomb cells — while hexagonal, the rectangular grid pattern appears in crystal structures
- Leaves — many plant leaves approximate rectangular shapes
- River floodplains — often form rectangular plots of fertile land
- Urban planning — most city blocks follow a rectangular grid layout
Rectangles in everyday life
- Rectangle body shape — in fashion, a rectangle body type has similar bust, waist, and hip measurements
- Rectangle pool — standard swimming pools are typically rectangular for efficient lane swimming
- Rectangle tablecloth — dining tables and their coverings are usually rectangular
- TV & phone screens — virtually all displays are rectangular
- Books & paper — standard page sizes (A4, Letter) are all rectangles
- Bricks & tiles — building materials are manufactured as rectangles for efficient stacking
- Football field — sports fields are typically rectangular (100 × 53.3 yards in American football)
How to Use the Rectangle Area Calculator
- Enter the length (a) — the longer side of your rectangle.
- Enter the width (b) — the shorter side of your rectangle.
- Select your units:
- Metric: millimeters (mm), centimeters (cm), meters (m), kilometers (km)
- Imperial/US: inches (in), feet (ft), yards (yd), miles (mi)
- Click "Calculate" — instantly get the area, perimeter, diagonal, and aspect ratio.
FAQs
What is the area of a rectangle with length 10 cm and width 5 cm?
Area = 10 × 5 = 50 cm². The perimeter would be 2 × (10 + 5) = 30 cm, and the diagonal would be √(10² + 5²) = √125 ≈ 11.18 cm.
How do I find the width if I know the area and length?
Rearrange the formula: b = A / a. Simply divide the area by the known side length.
What is the difference between area and perimeter?
The area measures the surface inside the rectangle (in square units), while the perimeter measures the total distance around the rectangle (in linear units).
What units does the calculator support?
The calculator supports both metric (mm, cm, m, km) and imperial/US (in, ft, yd, mi) units. The area result is shown in corresponding square units (e.g., cm²).
Can I use this calculator for a square?
Yes! Simply enter the same value for both length and width. The calculator will compute the area (a²), perimeter (4a), and diagonal (a√2) of the square.
What is the golden rectangle ratio?
The golden ratio φ ≈ 1.6180339887. If the longer side divided by the shorter side equals approximately 1.618, you have a golden rectangle. Our calculator highlights this automatically!