Area of a Rectangle Calculator

The area of a rectangle is the amount of flat space inside four right-angled sides. Calculate it with A = l × w, where l is length and w is width. Multiplication works because a rectangle can be divided into rows and columns of equal unit squares. A shape measuring 6 units long and 4 units wide contains 6 rows of 4 unit squares, or 24 square units. The result uses squared units whenever the dimensions carry a measurement unit. Length and width can represent whichever pair of adjacent sides you choose. Calling the longer side the length is conventional but not mathematically required. Reversing the two values produces the same area because multiplication is commutative. Both measurements must use the same unit before multiplication. If length is given in meters and width in centimeters, convert one measurement so the units match; otherwise the number has no consistent area unit. This calculator also returns perimeter and diagonal length. Perimeter is the total distance around the rectangle and follows P = 2 × (l + w). It is useful for estimating fence, edging, trim, or frame material. The diagonal joins opposite corners. By the Pythagorean theorem, its length is the square root of l² + w². A 12 by 5 rectangle has a diagonal of 13 because 144 + 25 = 169 and the square root of 169 is 13. Rectangle calculations appear in flooring, painting, landscaping, screen dimensions, fabric cutting, property plans, and classroom geometry. For flooring, multiply the room length by its width to estimate surface coverage, then add an allowance for cutting and waste. For a wall, use the same area formula and subtract windows or doors separately. For a frame or border, perimeter is usually the more relevant measurement. Knowing which measurement a project needs prevents buying material based on the wrong formula. Decimal dimensions are fully supported. A tabletop 1.8 meters long and 0.75 meters wide has an area of 1.35 square meters. Measure each side to an appropriate precision and round only the final result. Because area is a product, measurement uncertainty in either dimension affects the answer. The calculator preserves useful decimal precision, but the displayed digits should not imply more accuracy than the original measurements. A square is a special rectangle whose length and width are equal, so this calculator also handles squares. Enter the side length into both fields. Conversely, if area and one dimension are known, divide the area by the known dimension to find the missing side. These related formulas make rectangle area a foundation for coordinate geometry, construction estimates, algebra, and many practical planning tasks.