Rectangle Area Calculator

Multiply the length by the width: $A = l \times w$. For example, a $5 \times 3$ m rectangle has an area of 15 m². Both measurements must be in the same unit.

Area measures the space inside the rectangle (in square units), calculated as $l \times w$. Perimeter measures the total distance around the outside (in linear units), calculated as $2(l + w)$. A $5 \times 3$ rectangle has area 15 but perimeter 16.

Use the Pythagorean theorem: $d = \sqrt{l^2 + w^2}$. For example, a $3 \times 4$ rectangle has diagonal $= \sqrt{9 + 16} = \sqrt{25} = 5$. The diagonal is always longer than either side.

A square. Among all rectangles with the same perimeter, the square encloses the maximum area. For example, with perimeter 40: a $10 \times 10$ square gives area 100, while a $15 \times 5$ rectangle gives only 75.

Order 10% more than the calculated area to account for cuts, waste, and future repairs. If the room is 15 m², order materials for 16.5 m². For diagonal or herringbone patterns, add 15-20% instead.