Area of a Rectangle Calculator
Whether you need to know the area of a carpet, a land parcel, a TV screen 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) and A (area).
Take a look at the trapezoid and circle calculators for other geometric shapes, or keep reading to learn how to find the area of a rectangle!
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, it is called a square.
Our area of a rectangle calculator uses the following formulas:

For the area:
A = a * b

For the perimeter:
P = 2 * (a + b)

For the diagonal:
d² = a² + b²
If you're interested in 3D solids rather than twodimensional shapes, check out the surface area calculator.
Rectangle calc: find A (area)
 Choose the length of the rectangle  for example,
a = 5 cm
.  Decide on the width of the rectangle  for example,
b = 6 cm
.  Multiply these two values:
A = 5 * 6 = 30 cm²
.  The area of the rectangle is 30 cm².
Rectangle calc: find P (perimeter)
 Choose the length of the rectangle  for example,
a = 5 cm
.  Decide on the width of the rectangle  for example,
b = 6 cm
.  Add these two values:
a + b = 5 + 6 = 11 cm
.  Multiply the result by 2:
P = 2 * 11 = 22 cm
.  The perimeter of the rectangle is 22 cm.
Rectangle calc: find D (diagonal)
 Choose the length of the rectangle  for example,
a = 5 cm
.  Decide on the width of the rectangle  for example,
b = 6 cm
.  Calculate
a
to the power of two:a² = 25 cm²
.  Calculate
b
to the power of two:b² = 36 cm²
.  Add these two values:
a² + b² = 25 + 36 = 61 cm²
.  Finally, take a square root of the result:
d = √(a² + b²) = √61  7.81 cm
.  The length of the diagonal is 7.81 cm.
Naturally, instead of calculating all of these values manually, you can go ahead and use this area of a rectangle calculator. You can also use it in reverse  for example, to calculate the width of a rectangle with a known length and perimeter.
Golden rectangle
A special type of a rectangle, called the golden rectangle, is shown in the image above. Such a rectangle fulfills the following condition:
(a + b) / a = a / b = ϕ
where φ is the golden ratio equal to 1.618.