What Is the Surface Area of a Rectangle?
The surface area (more commonly just the area) of a rectangle is the amount of flat space enclosed inside its four sides. Because a rectangle has opposite sides of equal length, its area is found simply by multiplying the length by the width. This calculator does that for you instantly and also reports the perimeter so you have the full picture in one place.
How to Use the Calculator
Enter the length and the width of your rectangle in the same unit (centimetres, metres, inches, feet — whatever you like). Press calculate and you'll get the area in square units of that same measure, along with the perimeter. If you measured in metres, the result is in square metres; if in feet, square feet.
The Formula Explained
The area formula is $$A = \text{Length} \times \text{Width}$$ Multiplying the two side lengths counts how many unit squares fit inside the shape. The perimeter, the distance all the way around, is $$P = 2 \times \left( \text{Length} + \text{Width} \right)$$ because you walk along two lengths and two widths.
Worked Example
Suppose a room floor measures 10 m long and 5 m wide. The area is $$10 \times 5 = 50 \text{ square metres}$$ The perimeter is $$2 \times (10 + 5) = 30 \text{ metres}$$ So you'd need 50 m² of flooring and 30 m of skirting board.
FAQ
What units does the result use? Whatever unit you entered, squared. Feet in → square feet out.
Does it work for a square? Yes — a square is a rectangle with equal sides, so enter the same value for length and width.
What is the difference between area and perimeter? Area measures the space inside the shape (square units); perimeter measures the distance around its edge (linear units).
